Recently I've had a problem with Halo PC. The menu looks all white and playing ingame is also very different. I have had this problem before, but updating my video drivers fixed it. I currently have the most updated drivers for my ATI Radeon X1550 graphics card. Something that is very weird about this is that when I log onto another user on my computer, the problem isn't there, and Halo looks normal. I just spent about an hour reinstalling my video drivers. I also spent quite an amount of time replacing the maps with my backups. I also replaced bitmaps.map and ui.map from my CD. I have Windows Vista.
Anyway, here is a few screen shots to show you what it looks like.
White Menu
Ingame
My video settings are all set to high, with a resolution of 1280*1024, and a refresh rate of 60Hz.