I started having problems with my PC a few time ago for unknown reason. It can freeze all the time, but the most annoying is I can't install big programs anymore. It can freeze after a few seconds as well as after a few minutes. For example I'm unable to install windows xp sp2 because it wil always freeze at some point.

I have no errors, no blue screen... the pc just stops responding, sometimes the screen becomes black and I'm forced to push "reset".

I tried everything I could
-changed my power supply
-tested my hard disk, the memory and the processor
-disabled my sound card
-formatted my hard disk and reinstalled windows xp

I managed to install directx 9, also most critical updates, win sp1 and a game and I thought the things were fixed. However it started to freeze again.

During installs, programs scans (like virus scan) it will always freeze (and there are no errors when I look into eventvwr)...

My configuration is:
- athlon 1600+xp
- 718RAM
- 40GB Maxtor hard disk
- MSI k7t266 pro2 main board
- hercules 3d prophet geforce3 ti200 video card

Just a thought:

Had something similar with my system. Freezed for no apparent reason.
Was wondering why it happened until i figured that there was a thermal problem causing the system to get stuck. Just to be sure, check your CPU and Mobo temperature and see if they are unusually high

Yes, I forgot to mention it, but it was the first thing I checked... The temperature is ok (I don't overclock, the fans are all working and the freeze is happening even at the beginning of a session).

PS. The strange thing is I can work without problems for hours, however as soon as I'm using a program accessing my hard disk for too long it will freeze (installing, scaning something).

Try running your hard drive diagnostics. Here is a list:

http://www.tacktech.com/display.cfm?ttid=287

Yes, I already checked my hard disk with PowerMax and everything was ok...