WinXP and opengl problem


I just reformatted and installed WinXP.I am not getting any opengl support whatsoever.Here’s my specs…

AMD K6-2 400MHZ on Asus P5A-B motherboard
Asus Geforce v6600 SGRAM
256M RAM
SB Live Platinum

I first installed the Asus 6.49win2k drivers for my video card and I get to run in opengl for about 5 minutes,than my pc automatically reboots.I than uninstalled those drivers and installed the detonator 28.32win_xp drivers.Games now work,but no opengl support.I get an error"OpenGl is not supported by your card"(this is error I get for Halflife).I also installed the ALI AGP drivers and still no good.Any suggestions?