display goes black in a few seconds after I turn it on!

Hi everyone!

My friend and i are having problems with his LCD from Dell. Its a pretty old model but still would be great if could fix it)

So the problem is that when we turn the display on it stays that way for only a few seconds, and then goes black. Colors are ok, picture too... In these few seconds we can move the mouse, open a folder.., and the screen responds fine...

Another strange thing about it is that when my friend went mad about it he started clicking the on off button, and all ofa sudden it started working proprly!Oo But sure u cant leave it on forever..) So after tried turning it off and then on again the problem showed up again:(

Any ideas?Oo Thx in adv.:)