I installed debian 3.1rev1 and now I have two problems: the first is that everytime I reboot and gnome loads, i get messages which say that workspace selector and some panels have quit unexpectidely. It's not much of a problem, but it's still annoying. The other is that from time to time the monitor goes black (as if it was in standby mode), everything stops (for example, music stops playing), then the internal speaker beeps and after a few seconds the monitor turns on again, as if nothing happened and the computer continues working, the music continues playing from the place it stopped. This happens about twice per hour.
Any help would be appreciated.

cant help much with the first issue, but that second one sounds like bad hardware.

But earlier everything was alright, I was using ubuntu, slackware and didn't have such a problem.

Possibly power saving settings are off. It could be trying to shut down an active hard drive and realizing it's mistake. Power management problems upset one of my machines and it kept trying to go to sleep solely on the time settings, ignoring activity. I may be way off in left field but it may help.

That's exactly what I was thinking about in the beginning, but I tried to disable power saving in some screensaver properties, but it wasn't of much use. Any ideas how I can disable power saving?

depending on your GUI it should just be right click and configure desktop... also double check the system time and make sure it is not way off. i have had that be an issue under linux times. specially when my CMOS battery is low or needs replacing.