Have you tried to change your UT video drivers/rendering Clicking on START/PROGRAMS/UNREAL/TOURNAMENT/SAFE MODE.Then on the next screen Click on "Change your 3D device"It will most likely default to what the game thinks are the "best" device for your card.Or by clicking on "Show all devices" and selecting the driver/rendering device that you want to use.
If you have then it's:
a.Your drivers and/or 3D device may not working properly.
b.Remove Strike Force and reload it using the following suggestion.(d.)
c.Check out the Strike Force website and see if you can find an answer there.
d..UT might be corrupt in some way.
You can try un installing the drivers and going back to what you were using before updating them.(If did that recently that is)
Or you can try un-installing UT,Deleting the UT folder completely from your hard drive.
(the un-install does not remove everything from your drive)
Run a scandisk,then a defrag and reinstalling the game.
Only thing left is to be sure you have the latest version of DirectX.
Here's a few links you can also try.(I am presuming that you checked "Planet Unreal's" troubleshooting/FAQ already.)
EpicGames Faq
Unreal Tournament Faq
Ina-Support
Hope this helps in some way.