Screen Briefly Flashing Black

Question

Over the last few days, I've developed a problem where my screen intermittenly goes dark for a period of a second or less. This will happen three or four times in succession and then things will revert to normal for a few minutes. The dark periods are not uniform in length. I believe input is not frozen: if I am typing when the screen blacks out, everything I type is present when the display is restored.
My display is a 20" Apple Widescreen Cinema Display, less than six months old, connected via DVI to the built-in video card. There is a small light at the lower right that lights when the monitor has power but is not receiving a video signal--at boot time, or in sleep mode--and that light does NOT light up when the screen goes black.
I have searched all the log files in /var/log, /Library/Logs, and ~/Library/Logs, and none of them have any entries with timestamps matching the black-screen episodes.
I do have a different screen problem that MAY be related. Intermittently, over the last several months, I've noticed that when the screen saver tries to turn on, it fails--the machine repeated flashes back and forth between the normal screen and the start of the screen-saver, at even intervals of about a half-second. When this happens, it generates error messages in /var/log/windowserver.log repeating the lines:
Jul 01 00:09:21 [66] "loginwindow" (0x4c03) set hot key operating mode to all disabled
Jul 01 00:09:21 [66] Hot key operating mode is now all disabled
Jul 01 00:09:21 [66] "loginwindow" (0x4c03) set hot key operating mode to normal
Jul 01 00:09:21 [66] Hot key operating mode is now normal
Often when this happens, I need to log out and back in again to make many key shortcuts work (including Exposé and cmd-shift-Q to log out).
Has anyone run into something like this? I have a copy of Leopard on the way, but it's getting hard to work with the intermittently blacking-out screen.
Dave

Answer 1

An update--still leaving this "unanswered" because I haven't reached a final resolution.
I'm almost certain it's a hardware problem--I booted from the Tiger DVD and experience the same issue, so it's not the software.
In an effort to determine whether it was the video hardware or the monitor, I took the monitor in to my office (where I have a docked Dell laptop) and brought the Dell monitor (same size, also uses DVI connection) home. For about three days, I had no black-out incidents in either location.
I swapped the monitors back last night and have not yet encountered the problems. The only differences I can tell between how the Apple display was hooked up at home and how it was hooked up at work are that (a) the work machine has no Firewire, so the firewire plug was left hanging, and (b) the monitor USB was connected in both places, but at home, I connect my mouse and keyboard to the monitor USB and at work they were connected to the computer/dock directly.
The monitor is now set up exactly as before--FW plugged in, USB plugged in and supporting mouse and keyboard--and when and if the problem reappears I will start varying those connections.