Unknown Causes of Crashes

Hiya,

My computer is running standard Windows 7 Home Edition (64 bit) and I have been having some problems with it recently.

1. Windows Explorer crashes when I try to access files from My Documents, My Music etc. This only seems to be when I access them from the start menu. If I go via My Computer > Users etc all is fine.

2. After a short period of gaming, the computer freezes and starts running unbelievably slowly. It is unable to create textures on games and all I can see is characters on a blue screen. I have tried this on Fifa 11 (which now does not run at all), Deus Ex: Human Revolution, and Counterstrike: Source. It seems to be fine with browsing and low-end programs though, so I can listen to music and use the internet all fine. All of the games are legally bought etc and worked fine. I left my computer for a few months while away and nothing has changed on it apart from a few windows updates.

Are these problems linked? And what on earth is going on with my PC?