Yeah, i assume there is nothing wrong with your Xwindows system.
Using the new ATI drivers? they are *experimental* try running the card under VGA or Vesa compatibility mode.
You may have to adjust the cards dot clock to be within the parameters for your monitor. This is in XF86Config... heres a page on that...
XF86Config info... may be useful
Hope that helps.
Also if your card has several outputs, the glitch may be in that it is sending the output signal to the wrong one... although this would be very strange. I would hook each one up and test to see whether you get an image.
Good luck
