I'm going to assume you have the ATI drivers
installed for your card. Are you able to change the resolution manually by going into Windows control panel\Display settings, or the Catalyst control panel?
If you aren't able to change the resolution using the OS or driver
controls, it might be a hardware issue, or it could be the drivers. 640 x 480 is like the default resolution. All monitors support it, and it's usually what the BIOS screen comes up as. It's a failsafe, to give you a raster (picture) if something goes wrong with your drivers, or with a Windows install, when drivers haven't been loaded yet.
If you have access to another computer, try plugging the monitor into it, and see if it displays at the proper resolution. If it works, that rules out a monitor issue. By the sound of it, though, it looks like the monitor may be the problem, since it's happening with another card.
I see that your cooling is listed as none. I don't know if you're overclocking the video card, but if you are, without half decent case cooling it may be stressing the card too much if the extra heat can't be exhausted from the case. With electronics, heat is the enemy.
If the monitor works right on another PC, post back with some details of what happened, and we'll see if we can be of more help.