Update: Not fixed. it froze about five minutes after I successfully made the remaster. I checked in Bios during reboot and temps for my AMD Athlon were normal, CPU-39°/MB-37°. I had RPM reading on both fans so I assume they are working.
Checking the BIOS means shutting down at which time whatever was causing the problem has gone.
You need to run something to monitor such things as temperature, running processes etc while using the PC, so that you can see what may be causing the freeze.
Obviously it is not the remastering itself that is causing it - with this latest info - so it is unlikely to be temperature related. Nonetheless it is a good idea to monitor temp as well as other things.
Watching the running processes could give an indication if one of them is consuming too much resources, which might be the cause also.
What apps are running when it happens?