How to fix Imac 8.1 on Windows black screen problem?

Firstly when I originally got this machine it seemed (about 4 years ago), sometimes had my Pc forget the keys shortcuts for the Mac)
Anyway over the last year I have the problem where I'd be in the middle of doing something on the Windows side then randomly go black. Strangely this doesn't effect the Mac side on my Boot Camp.

After some testing on the Windows side I noticed this screen doesn't force the black screen when I'm either watching a video using 'Media player' or playing a game like 'STO' or 'KOTOR'. Also I wouldn't mind the black screen if it was temp but the thing is it stays black until I hard-reset the Imac.

Anyway does anyone have any idea's on how to fix this? It's been a problem for the Windows side for a while, haven't had much luck trying to fix the issue so the video playing 'idea' was always a temp solution till I can find a way to fix the issue. (The problems exists on both Windows 7/8 but now using windows 8 again because had to replace my broken hard drive recently).