I have Fedora Core 5 (I know, it's old - I plan to upgrade soon).

I have a Diablotek V7500-128A (ATI Radeon 7500 128MB AGP4X) video card.

At the Gnome login screen, it will eventually time out and put the monitor into
some kind of sleep mode. Most of the time, a wiggle of the mouse will wake it up.

Sometimes, though, it won't wake up. I have to reboot the PC to wake it up.
I can actually soft reboot by entering Ctrl-Alt-F1 then Ctrl-Alt-Del since I
can't see the screen, and this will wake it up after the reboot occurs and the
BIOS starts up. So a hard reset is not necessary.

Any ideas what causes this?

Also, where in Gnome can you alter the power saving settings for gdm?