I am running a fresh install of Ubuntu 12.10 with Cinnamon,

after roughly 10 minutes the screen turns black. I have set "Turn screen off when inactive for:" to "Never" or tried high values (1h +), this does not affect this behaviour.
In the dconf-editor I located following entries:

org.gnome.settings-daemon.plugins.sleep-display-ac

setting to 0 did not have any effect

org.gnome.desktop.applications.screensaver.idle-activation-enabled

unsetting/unchecking did not have the desired effect

org.gnome.desktop.applications.session.idle-delay

setting it to 0 or very high values (100k) did not have any effect.

do you have any suggestions on how to approach this issue?
cheers
peter