Game(s) freezes and doesnt load graphics but can hear the sound

[Minime88]

Everytime I play Call of Duty 2, Battlefield 2, Half Life 2 & Mods the game won't start - it just freezes. I enter the server and the game freezes. Half of the games graphics load and theres a lot of flickering. I can still hear the sound. I have played these games before on this very same computer in the past and they worked fine.

I have a Radeon 9700 PRO video card. Pentium 4 CPU 3.2 GHZ, 1 GB of ram Microsoft XP Home Edition SP2

Please help, I want this problem sorted out before I get Oblivion.

Thanks.