Q: G4 PPC, display has bad stripes - monitor or the card?

I've got a G4 PPC tower, using OS X 10.4.11 (Tiger) with a NEC monitor and ATI Radeon 9800 Pro card. After a planned power outtage in my town, the monitor looks totally wonky after starting up again. There are vertical cyan stripes made of short horizontal lines on light background areas, and red stripes on dark backgrounds. Is there a way to test to see if it's the graphic card that's doing this? On start up the display looks correct (although it displays a warning that the display is not connected), but it reverts to this weirdness once I get to the desktop. Also, how can I get the resolution reset to its original 16:9 ratio, millions of colors, 60 hz? I was "fiddling" with some of the display options; first it went to 800 x 800 stretched and now it's too fine and doesn't fill the screen like it did before.

Here's a screen shot: (my screen saver is a slide show of some knitting projects, but you can see the red stripes on the black pants.)