If you reloaded software (and you are not on the default VGA port) and you are hooked up to the S-Video output you probably have the black screen issue.http://forum.linuxmce.org/index.php?topic=3931.0
"the page is very long, what do I have to search for exactly?" if you mean the var/log/Xorg.0 file you'll be looking for "Mode Validation" i.e. which mode is valid and which is rejected. After the ModePool section ends the assigned Display Device will tell you screen resolution.