Half-life (OpenGL problem)

Hi all,
I’m just registered here 'cause my hope is dead -_-

When i try to play in OpenGL at Half Life-counter strike- game, he say me “OpenGL is not supported by the video card”… But is wrong, i play in much more game without problem…
I formatted just 3 days ago and i installed only HL, quake and Matlab(math software)… Well i played for 3 days without problem, but this EVENING ONLY half life-counter strike- start to broke balls
(the others game work very well)

Pls anyone can help me? The system is
WinXP pro edition
Geffo4 ti4200 with Detonator 45.23
bye

P.S.I just tried to uninstall and re install half life+ counter strike, but nothing… Just tried to uninstall detonator and reinstall, but nothing !!

PLs HELP ME!!!

thx )

yeah me too, i have this problem for months and months now because i couldnt find a fix for it. some say its because of winxp.
so i havent played HL and CS for a long time now since i upgraded to G4 ti 4200.

UP
help pls