Windows 7 Windows Update Runs Forever After Clean Install

Hi and welcome to the forum

To answer your question briefly, it depends. On what version of W10 you actually have. There are many going back to last July 29th (v1511 b10240.x). If you attempted to install the Aug. 2nd Anniversary Update from ISO file, that would have worked, and the update shouldn't take 5 hours if your hardware is working correctly. Mine took about 2 hrs. or so.

Also, it's customary when you ask a question here about your computer that we have some basic information about it. Is it a desktop PC or a laptop? Is it an OEM computer (Dell, HP, Acer, Toshiba, Samsung, etc.)? Or is a self-built PC or a custom-built PC? If self-built or custom-built please provide full hardware specs including Make/Model of your Motherboard, Make/Model of your GPU card, Make/Model of you bootdrive hard drive, Make/Model of your PSU and Wattage. If you don't have this information handy, you can go to piriform.com and download the free SPECCY diagnostic. Run SPECCY and post the resulting output text file back here to this thread.

Why were you doing a clean install on your computer? Did you have a hard drive crash, windows crash, etc.? It would be helpful to know the version of W10 you were on prior to the update attempt: such as v1511 b10586.545. You can use the <windows-logo-key + R-key> command to get the run box, type in "winver" Windows will give you the exact version and build of W10 you have on the machine. If you can't go forware with the update after 12 hrs., use your Clean Install boot-media and go into Recovery Options and back out of the update, try System Restore, etc. If that doesn't work you could have accidentally gotten the Anniversary Update (AU) which has crashed at least 2 computers we know of.

When you ran your clean install, did you remember to run the W10 COMPATIBILITY test to check for outdated drivers, apps, and hardware?
If you we suggest you do this prior to completing another clean install. Instructions on how to run the test are here: Get Windows 10 app - Check Compatibility Report for Windows 10

Please answer some of these basic questions for us, especially your hardware specs and we can then advise you further. If you run the clean install again, you should consider using the ISO file from here: Microsoft Update Catalog
This will install the newest AU update (KB3176929) on your computer. The build number may be different a bit, but the latest I have here is v1607.b14393.51 as of today.

We can then advise you further.
Cheers!
<<<BIGBEARJEDI>>>

Running Win7, ver 6.1 SP1. Not trying to update to Win10, staying with Win7.
Dell XPS 8700, 8GB.

Recovered using original Dell recovery disks to new drive because was hit by ransomware. Don't trust old drive, pulled it. Have data backed up from before being hit.

Problem is Windows Update won't update, just churns.

There have been some incredible long waits for WU in Windows 7 and 8. I had one time 36 hours before available updates even came up and then another 24 hours to install same. I tried every so called fix available and none of them worked except for patience oh and shutting Power Options in Control Panel to "always on" so you have a chance.