Graphic glitched when playing games appeared after a period of a perfect gameplay.

Hello.
I started using Parallels a while ago. I needed it to run GTA: San Andreas and it did - flawlessly. After some time, however, the textures started to blink in many different colors, so the game started to look crappy. It didn't bother me that much so I left it as it was. I'm not sure if I installed or changed anything at the time it started.

It bothers me now though, because I tried installing Simcity 4 and this game is very ugly with that bug, to the extent of being almost unplayable:


So I wonder if there is anything I could try doing to find out what causes this?
Thanks in advance!