Comment 15 for bug 844241

Experiencing almost the same here. After 10 minutes of inactivity, the screen turns off. When moving the mouse, only the cursor is visible. The rest of the screen looks like the backlight is off. When pushing Alt+Ctrl+F1 and then Alt+Ctrl+F7, the brightness is restored. No login screen was displayed. I have the same isue when locking the machine, cursor stays visible, rest not. Typing password+enter restores visibility again.

System;
Ubuntu 11.10 x64
Intel® Core™2 Quad CPU Q9550
ATI Radeon HD 4870 X2 (fglrx 11.12) - one monitor

End of syslog;
Jan 7 12:59:27 dennis-desktop kernel: [ 3241.524210] gnome-screensav[2344]: segfault at 5 ip 00007f1793d39859 sp 00007fff5a342a00 error 4 in libcairo.so.2.11000.2[7f1793d00000+b9000]
Jan 7 12:59:27 dennis-desktop gnome-session[2262]: WARNING: Detected that screensaver has left the bus
Jan 7 13:17:01 dennis-desktop CRON[3886]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly)
Jan 7 13:22:06 dennis-desktop kernel: [ 4600.536160] vgaarb: this pci device is not a vga device
Jan 7 13:59:17 dennis-desktop kernel: [ 6832.000641] vgaarb: this pci device is not a vga device
Jan 7 13:59:18 dennis-desktop kernel: [ 6832.494666] gnome-screensav[3983]: segfault at 5 ip 00007f9c72ab6859 sp 00007fffc0aeb390 error 4 in libcairo.so.2.11000.2[7f9c72a7d000+b9000]
Jan 7 13:59:18 dennis-desktop gnome-session[2262]: WARNING: Detected that screensaver has left the bus
Jan 7 14:16:02 dennis-desktop kernel: [ 7836.126481] vgaarb: this pci device is not a vga device
Jan 7 14:17:01 dennis-desktop CRON[4442]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly)
Jan 7 14:25:49 dennis-desktop kernel: [ 8423.137963] gnome-screensav[4746]: segfault at 5 ip 00007fd3cc610859 sp 00007fff30c4e370 error 4 in libcairo.so.2.11000.2[7fd3cc5d7000+b9000]
Jan 7 14:25:49 dennis-desktop gnome-session[2262]: WARNING: Detected that screensaver has left the bus