Comment 1 for bug 156429

Confirmed.

The same problem with Kubuntu 7.10
Driver "radeon"
Card Radeon 9100

Temporary solution :
1. CTRL+ALT+F1 (go to console)
2. ALT+F7 (go to X org)

Hint:
Driver (?) didn't set up proper resolution/refresh rate ,
when changed in display settings (even to the same param.)
after confirm to change resolution screen goes black and monitor turns off.

Want more information?

Best regards
Cactus

Ps. For me display manager in kubunt is sick. Never work as prefer.
Better is krandrtray alwas work perfectly. Need to check in new kubuntu.