Has anybody managed to use the N800 while the power-cord is connected while at the same time beeing charged? The problem I have is that when I am using the tablet and Low Battery alert comes up then I connect the power-cord everything blanks out while charging. I still want to use it while charging..

Mine works fine while being charged - no screen blanking. The behaviour of your device is not normal.

So after you connect the power-cord do you press the power button again or your still there where you were at? Maybe I am missing something...

I don't press the power button (assuming the device is already active). If the battery becomes low when I'm using the N800 I just plug in the power cable and the only visible screen difference is that the battery in the status bar begins to "fill up" as the device is charged. There may also be a brief on-screen message in the top right corner confirming the device is now being charged.

Unfortunately I don't know what to suggest as the problem you describe is quite unusual and I've never seen it reported before. Have you tried reflashing the device just in case a software setting has somehow become corrupt?