Windows 7 Ultimate won't start

Sep 16, 2018
I need help with this one.
I have a old pc that I thought it was broken but it was starting up and the monitor showed no signal.
So I bought a new one and kept the old one.
The new one was working fine until now.
I thought that maybe I should take the hard drive back from the old one and put it in the new one to move some files onto a usb stick.
Got it done, they were compatible and all but windows 7 won't start.
I saw this and said that maybe it's not compatible.
I put the original hard drive in and again, windows 7 won't start.
I tried startup repair, system restore, windows memory diagnostic and some YouTube tutorials with the command prompt, nothing worked.
I have on the new pc Windows 7 ultimate 64 bit. On the old one Windows 7 home 32 bit.
The hard drive is connected properly and I don't want to reinstall Windows.
Please help me to fix this issue on the new one and help me out with the old one as well.
Have a nice day!