When you say "Activation Code" , I believe you are referring to the Windows License Key (COA-Certificate Of Authenticity) sticker. Haven't worked on many All in Ones, but I did work on a Dell All in One 2305 last year and disassembled it for parts. The Mobo is hanging on my wall. If I recall, the COA sticker was on the screen bezel snap-on piece on the bottom of the rear assembly. I think it had the License Key on that snap-on piece. I think it was for Win7 Pro as this machine was like 3 yrs. old now.
Just so it's clear, Microsoft does support Win8 & Win8 Pro upgrades to W10, but you do have to upgrade to Win8.1/8.1 Pro to do so. Some guys here have had luck with bypassing the 8.1/8.1 Pro upgrade, but it's not easy, and doesn't always work. Unfortunately, this is 1-2 days of time-consuming downloading of updates to get your system from 8/8 Pro to 8.1/8.1 Pro. Once you do that on your new hard drive, you can then easily upgrade to W10 Pro. Once that's done, you also have the option to wipe that drive clean and perform a W10 Pro clean install, since your Dell XPS is then registered with the Microsoft Activation Servers.
After re-reading your Post 3 times, I'm having a hard time understanding what it is you are trying to accomplish. You do wish to upgrade to W10 correct? And you want W10 to be Activated and Licensed now, correct? If the answer is YES to both of these, options above are posted to do this legit way. Of course, you don't have to Activate your W10 Pro to use it now. That doesn't have to be done until after July 29th 2016. I currently have 4 machines with W10 (2 with Home & 2 with Pro). Only of those is Activated & Licensed (my Sony laptop) from a Win7 Home upgrade. And frankly, I don't see any difference running my other 3 non-activated machines (2 laptops & 2 desktops). I understand your wanting to make it legit--that's admirable. Not necessary really, unless you are running some corporate software such as VPN, or Exchange E-mail or something.
On a modern machine, you can simply download the free W10 Pro ISO file from Microsoft website, and BYPASS the 8/8.1 Pro upgrade altogether. Just do a Clean Install on your Dell's new hard drive of W10 Pro. You'll have to buy a W10 license between today and July 29th 2016 as I mentioned above, whether or not you do an upgrade from 8/8.1 Pro or not, and then license the newly upgraded W10 Pro anyway. Why hassle with the upgrade?; just do a Clean Install, buy a W10 license on the Internet; you can find them cheaper than the $199.99 list price now, just make sure you use a reputable company for the W10 license purchase such as CDW or NEWEGG.
Lastly, you can go to START-->RUN and type in the Command "System Information" and Windows will tell you exactly what processor type your machine has (32bit or 64bit). If you've got 8/8.1 Pro already installed on that new hard drive, this is easy and will facilitate your upgrade or purchasing the correct W10 Pro license on the Internet. Alternatively, you can download the free SPECCY program from piriform.com and it will also tell you this, as long as you have any modern version of Windows installed on the new hard drive.
Hope that helps.
<<<BIGBEARJEDI>>>
