Problems with UT

My problem is when I play UT in Direct 3D using any resol, 16 or 32 bit color and textures and world detail on any setting. . My screen starts to blink, but usaully I start a game anyway. And everytime about 15 seconds into play, the game just freezes and crashes my computer. I have simarliy problems when playing other direct 3d games. But no problems when I use open gl. I cant figure out whats the problem, Ive configured my direct 3d setting in the nvidia menu many of times and get the same result. None of my hardware is overclockd.
AMD T-Bird 900mhz
Nvidia GeForce 2 GTS
160pc133
My destop resol. 1024x768 32 bit color
ps. I have all the newest Via drivers and I have UT version 432

Thanks anyway

Thanks for your help, but no cigar. Now I have another problem after about 5 seconds into the game, the screen turns blue, while the music is playing. Im now begining to hate this game.

Thanks for your help I,ve solved the problem with the UT thing. Your right open gl does look more visually appealing, but only if you can see the srceen. Its so dark I have to guess where stairs and bots are.
ps. the brightness setting does'nt work.