Hello, I see you have no replies. Let's see if we can't add some info to get this kick started.
You have a screen saver chosen. When it kicks in the screen just goes black. Can you wake the PC with mouse or keyboard at this point? You say "it makes me log on again". Let's get specific about what this means. You are unable to wake from this black screen, so must log on again? Using what method? There are certainly screen saver and power settings to explore, but lets get very specific, step by step, with any messages you see, etc. what happens.
The screen goes black after the period I have set for screen saver to come on. I have a screen saver set. After it goes black...
I think we can get you some help with more info. A Guy