Windows 10 Can I Use My Laptop's Windows 8.1 Product Key to Install from an ISO After Upgrading to Windows 10?

yes... as long as the 8.1 it came with was in fact the factory install then the key is still stored in the motherboard.

it may have been a w8 key that took the free upgrade to 8.1 (and then 10) in witch case you will need a w8 iso but you can then still upgrade that (still free) to w8.1 after activation and of course the option will always be there to just install WX later without needing to start back at w8 again i.e, your wx key remains linked to this laptop now.

p.s, it goes without saying but I'll still say it... make backups!
I suggest installing a fresh laptop harddrive to install your w8 | w8.1 on... that way you can just replace the wx hdd any time the [you know what] hits the fan.

Ok, thanks heaps

Here's a related question. Suppose I wanted to downgrade from the creators update version back to the anniversary version ( I think that was 1609). Is that a possibility, or is it asking for problems?

Hi Ed,
It's not easy, but it can be done. The issue is that if you upgraded your W10 CU on that computer more than 30 days ago, or you deleted any or all of the 3 windows.old directories used for W10 rollback, you can't use Microsoft utility to accomplish it. As long as all your stuff is backed up to external media as I'm always telling folks here, you could do it. The best way to do this is via a W10 Clean Install, you can go to the Microsoft Update Catalog, and download the W10 AU (v1607) ISO file, and burn it to DVD or USB media and run the Clean Install. Take a look at this link provided by one of our Admins (kemical) here: Microsoft Update Catalog

Personally, I really like Norway's idea that if this is your only computer, or your "daily driver", it would be worth some money to get yourself a new hard drive that you can experiment doing this on! Hard Drives are cheap; you can get a 500GB or 1TB drive for under $70 on ebay, newegg, or amazon. Remember, that if you impact your main computer, you may lose your Internet & E-mail access, along with the ability to access your online banking, government sites such as DMV or Social Security or IRS, or pay bills online with credit cards or make purchases with same.

Most of us W10 aficionados who are also Insider Testers such as me learned a long time ago, that fooling around with OS upgrades or downgrades on your only PC or your PC you use to run your daily life is a BAD IDEA IMHO. I have about 8 PCs that I use for doing this sort of thing-and they are all backed up with various Disk Imaging software on my network, so if I crash one of my test setups, it's no big deal, I can put it back in 1-2 hours. I also have like 5 hard drives with different windows versions for supporting my various customers with W7/W8.1/W10 and W10 in multiple versions. I can boot into any of those by switching some cables or my Boot Order; makes it really easy. This is probably way more than you need to do; but I'm explaining the process so you can understand WHY we do it this way. If you make a boo-boo on your existing computer attempting a downgrade and botch it; it could take you weeks or even months to get it back near to the way it is today.

Using a separate hard drive, or better yet, a separate PC or laptop for this experiment is what we really would recommend. If you go this way, and trouble finds you as you say, it's no big deal since it won't impact your main computer--you can throw it out the window if you want, but you still have your original hard drive with a working W10 config on it you can use for daily stuff; see what we mean??

Probably could have answered it shorter by saying; "maybe, depends on your willingness to experiment and how prepared you are--backups etc.". Hah!

Well, hope that proves insightful.
<<BBJ>>

@undercovergangsta784: Just a word of advice on the downgrade, if you have a Samsung laptop built between 2011-2012 you should know that if it came with W8 from the factory and that's the original license, you won't be able to upgrade to W8.1 as they skipped all support for W8.1 and jumped to driver-level support for W10 only--so there is no upgrade path there. You have to buy a brand new version of W10! This may not seem like a big deal; but some PC manufacturer's such as Samsung skipped W8.1 support, and applied their resources to update their computers to W10; good for them, really bad for customers. I spent 9 days getting a Samsung laptop upgraded to W10 from W8, and because all my other W8->W10 test upgrades all worked, I had never run into this particular problem and had locked in a price for the upgrade with the Customer. I had to eat the cost of a new W10 license in order to complete the upgrade! Arrghh! Thanks, Samsung!
Best thing to do is to check the COA sticker on your machine and see exactly what version of windows it came with. If it's W8.1, then the methods mentioned above will work in most cases. If it's W8, and you run into the problem I did with the Samsung, the Clean Install may not work for you. If this is a self-built or custom-built PC; all bets are off due to hardware driver support from your Motherboard manufacturer.

Best of luck,
<<BIGBEARJEDI>>

Thanks, Big Bear. As always, you, as well as the rest of the gang,offer sage advice. I've been thinking of getting another computer for my experimentation; to keep costs down, maybe a refurbished or used one. I wish I kept my previous Toshiba laptop, running XP. I got a lot of use from it. I know Toshiba isn't your favorite brand, but I've always gotten good service from the ones I had (4 of them).

You bet, HK, I appreciate your kind words. Yes, very good idea. Well, I bought 400+ Toshiba laptops at my last company where I was responsible for setting the standard for all desktop computers; like I said they used to be the standard against which all other laptops were measured worldwide. For your purpose, yes you can buy refurbished computers if you are careful. Best places to buy them are Best Buy, and Micro Center, both of which have online stores and brick-and-mortar stores in lots of states. They give you the best warranties, and they both have top-notch service centers and only employ A+ licensed and certified Techs (many whom I personally trained!).

A couple of notes; you can buy an XP laptop, as long as it was made in 2006 or later. Early 2007 was the last year XP computers were made, and that's the switchover year. Hardware-wise there are missing instructions in the CPUs before in 2005 or before which prevent computers of that age (about 12 years old) from ever working with W10. Most of my test PCs are built in 2007-2010, as they get junked by their owners, donated to me for parts or recycling when my Customers decide to upgrade to more modern computers. My primary desktop PC test machine just turned 10 years old last month (built June 2007), and runs 5 drives in it; 4 with W10, Linux (Ubuntu & Mint), and a W7 drive for supporting customers still running on W7. This machine I rescued from it's fate in the local dump, as my Customer bought a brand new Dell laptop about 3 years ago and gave it to me. I get a lot of computers that way, and years ago when I got to about 75 of them in the house, my wife made me clean them up and cut back. I now have 15 or so to keep things good with her!

If you like Toshiba laptops, you can pick up a late-model XP one built in 2006/2007, but better would be to get one that came with Vista, or at least one that had a VISTA READY or VISTA COMPATIBILE sticker on it but still has XP loaded on the hard drive. Those computers have the best shot at running W10 which from your posts is the version of windows you'd most like to experiment with. Interestingly, most of my test machines do not have W10 driver support on the manufacturer's websites, but yet if they are this age and were designed to run Vista in the future, most of those will still run W10 without too much problem.
Here's an example of a L305 Toshiba, with a dual-core Intel CPU I like: Toshiba Satellite L305-S5905 15.4" Laptop Windows Vista Intel Core2Duo 250GB 3GB 8839741590 | eBay
It's a little more than some of the Toshiba's that age, but at $250, it has a 64bit CPU chip, which means you can run both W10/W10 Pro 64bit and Linux 64 bit; which is a very desirable feature for testing more modern windows apps. Looking around you will find several for under $100 but the problem there is that their CPUs are usually 32bit (64bit CPUs in laptops back then were quite pricey), and you will have driver and app compatibility issues with W10. You can still buy a 32bit Toshiba laptop, but you'll have your hands full getting it to work.
Just some things to think about.

One last word of advice, and you may already know this, but if you buy on ebay in either BUY IT NOW or AUCTION format, make sure to check the seller's reputation and read the reviews from other customers who purchased from that seller. Notice the seller information on the posting on the link above; he has a 99.2% feedback rating. And has sold 50,454 items on ebay. A very experienced seller with a very high feedback rating is what you want. I rarely buy any computers or computer parts from sellers with anything less than a 99% feedback rating. I've been on ebay for 18 years, and still have a 100% feedback rating, which is not easy to do. Just be careful if you buy one from there.
A big bonus with buying low-cost used computers from ebay is that if you have a PayPal account setup, you get an automatic $1,000.00 insurance protection on all purchases below that amount which is where most used computers fall into the bucket at. If the seller attempts to rip you off they are risking their reputation (which is everything on ebay), and PayPal will still refund you the money if you are willing to go through the dispute arbitration process which I have done several times; and they almost always side with the buyer if a transaction goes bad, and the seller refuses to help you or refund you.

Let us know how it goes!
Have a great weekend.
BBJ

". I get a lot of computers that way, and years ago when I got to about 75 of them in the house, my wife made me clean them up and cut back. I now have 15 or so to keep things good with her!

Yep, Big Bear. Those wives can be really pesky at times (been there) That's why I like bachelor life. I can play with my computer to my heart's content whenever I want.

well wives are more fun to play with imo but each to their own mate.