Cannot get computer to sleep or shut down after upgrading to Win 10

Getting a strange problem on my HP desktop (p7 1126s) Pulled it out of storage, it was running Windows 7 Home Premium 64 bit. It was working fine, it was just really slow (as I remebered it).
I decided to upgrade to Windows 10.

I used the Media Creation tool and made a bootable USB and installed Windows 10. I did not do an in place upgrade.
I ran windows updates and windows store updates.

However, I cannot get the computer to shut down or go to sleep. If I go into windows and choose shut down or sleep, the screen will simply turn off. However the hard drive and the fans will still be spinning.
I cannot resume it from "sleep" unless I do a hard shut down of the computer (Sometimes I need to try a few times...)

I've tried turning off Fastboot/ sleep. But doing that doesn't fix anything, I cant shut down the computer.
I've even tried just reinstalling it again.

I've read that this was a rather common problem back in 2014/15... Considering this is a older PC (from... 2012?) Doesn't seem unlikely I would run into this problem.

anyone got any suggestions? Thanks!