Entire display corruption, DirectX at fault?

Sometimes my monitor's display will mess up at random, with
(this is hard to explain in words) garbled graphics
throughout the screen. If possible at all, continued use
is very difficult. Sometimes the monitor seems to go into
standby (on but not displaying), but I don't have any
standby options set. This usually happens during two times...
1. When I start my computer
2. While running the game program "Stepmania"
(www.stepmania.com)

It seems to happen more often with situation 2. To
elaborate, I'm running the program normally, then my
monitor messes up, but the music continues normally (to a
point, then it loops a short clip). This has been
happening anywhere from seconds to a minute after I start
the program. I think it might have something to do with
DirectX(9.0c), because I sometimes get the garble effect
when testing DirectX9 graphics in dxdiag. Help would be
extremely appreciated.