Try changing your renderer device, like Direct3D8 (which is downloadable at download.com i think) Or the OpenGL driver (found at unrealtournament2004.com) If the problem still persists, you may need to reinstall it.
thanks actually i wound up just reinstalling. it only took a few minutes and it reinstalled around all my mods and maps and patches and stuff so thank god i didnt have to start from scratch. still it was weird tho. i mean, it started between rounds out of nowhere!
I have had that issue when patching beyond V436 (eg:440,451). I am pretty sure any patches after 436 were really meant for servers. Others have had no problems at all with the newer versions. I, also, had to reinstall to rid myself of that problem. Two different times.(Hardheaded?) Both times it was right after installing the v451 patch.