Doom 3 settings getting reset

[pogoman59]

The first time I started up Doom 3 I was able to change the video setting with no problems. I just changed the resolution higher and increased Anti-Aliasing. I played the game on my souped-up computer with no problems. Now however the settings have been reset to 640x480 resolution and no anti-aliasing. I go to the settings and change them however whenever I exit DOOM and re-enter so that the settings will take effect the settings get reset again to 640x480 and no anti-aliasing! What can I do to fix this problem? Thanks for the help.