> Well, thanks for your help, but it's still not working. I don't get an error
> message at all. Just a blank (purple) screen and then after a while it goes
> back to the games list.
What game rom are you testing?
Try frogger, dkong or pacman. be sure it is a full rom and not a split or clone only. (Post here what your rom size is and what files are in the zip if you suspect it is not a full version).
Another way to test the rom is to install Mame32 on your desktop and do a rom audit to see if the rom verifies alright.
Hope that helps.