Need help, screen froze when playing games with ati9500pro @stock

Hi all experts, I just bought myself a new system and when I tried to play games like counter-strike or command & conquer: generals, the game froze within 30 seconds and all I saw was a screen of mess-up tiles. Anyone know what did I do wrong? I did not o/c my video card but I o/c my cpu a little bit from 2.4 to 2.7. I set my FSB to 150 to o/c my cpu from 2.4 to 2.7 and I lock the PCI to 33mhz fixed. And that’s all I did. Thanks for the help in advance.

My system:
P4 2.4B SL6RZ @2.7
512MB PC3000 Kingston HyperX DDR
Abit BH7 mobo
ATI 9500 Pro (Built by ATI)
Driver: Catalyst 3.2
Directx 8.1
WinXP Pro SP1