It is surprisingly easy to set your monitor contrast 0 and consequently black out your entire monitor using the ATI Catalyst Control Center for Linux.

It happened to me this morning while I was in the middle of finishing an assignment at the last minute.

press Alt+F2 (brings up the Run Application dialog)
type “gnome-terminal”
type “aticonfig –set-dispattrib=lvds,contrast:100″
press Enter.

If nothing happens, you probably made some typos. Try it again.

Alternatively, try a different display type. “lvds” is default for LCD screens; other possibilities are crt1, tv, cv, tmds1, crt2, tmds2, tmds2i, dfp3, dfp4, dfp5, dfp6.