It's a problem with Unreal Tour.
You might need to reinstall everything.
Did you overclock it?
Do you have the game on a separate drive?
Have you edited the game in any way?
UT No CD Patch
1. download UT 2004 No CD patch
2. put new UT2004.exe in your UT2004/system folder
3. when it asks to replace file, click yes
Hopefully this will fix your problem..