freezing and flashing

[ratmactivist]

after playing halflife 2 for a few minutes, no matter where i start, the screen starts to flash and then it just freezes. i have to manually reboot whenever this happens. ive updated drivers and toyed with all the video and sound settings, but it still happens.

ATI radeon 9200 128mb ddr agp
512 RAM
1.4GHz processor

please help!! :flame: