You ate in a bad place. Simply due to age. Motherboards do fail, gpus fail, anything that uses capacitors can fail, given time and use and exposure to heat.
Your motherboard is quite old, the psu is a known type to suffer failures, OS and drivers are no longer supported for fixes. Pretty much everything is starting to literally 'wear out'. So diagnosing any issues is extremely difficult.
The fix could literally be anything. Reseating ram several times, reseating the gpu several times, reseating the power connections to everything several times, just to wear away any built up oxydation on the pins.
Using DDU (guru3d.com) through safe mode, to remove and reset the registry entries, then reinstalling a freshly downloaded gpu...