Restart/Start issues

Hi, I'm new but I've been around a few times and I thank you all for the invaluable help and tips.
I just upgraded my Dell Optiplex 960 (ancient) Core 2 Duo, 8GB, to Windows 10 professional 64 (10.0.10941 build 10941) from 7 pro 64. I had to fight all the way through the install because it hung at the first restart. I finally got it installed through a little trial and error, but mainly by luck, with a cold start after initial step of install.
Ever since, I can only get Windows to boot with a cold start, and it has to be really cold, if I turn the PC back on right away it won't boot. (Sometimes the only way is to pull the plug!)
Actual symptoms are: hanging at the initial Windows logo with swirling dots for hours, or the PC saying that there's no boot device. Sometimes Windows seems to mess up the settings in BIOS and after I fix that it boots, but only if I shut the PC first and give it some time.
I tried disabling Fast Boot, and I reflashed my BIOS. Any help would be appreciated.

Compumind said:

Hi Schloz -

Welcome To Windows 10 Forums!

Could you please try this and let me know if it works?

Tails - Home

Thanks!

Try what?

Compumind said:

LOL. Installing Tails on a USB flash drive, per the link provided.

Is that your way of telling me not to bother getting Windows 10 to work on my old hardware?

Ok I'll try it. What info would you need from me once I boot from Tails?

Compumind said:

See if your computer boots normally from a cold start (enable USB boot or burn to a CD if USB boot not available.)
If it works, than you will probably need a clean install of Windows 10, if it is not a hardware issue.

I just booted the Windows 10 install media from USB, that's how I installed Windows 10. Does that tell you anything? Or does it need to be Tails?