Screen flickering

My screen starts to flicker from time to time. Sometimes during this it cuts to a black screen or even shuts down. Before it would change to a dark screen where you could just make out the image on the screen but would have to restart. I no longer run the mac solely from its battery because it is dead and have to use the mains adapter so I don't know if this could have something to do with it.

Any ideas many thanks?

I've just noticed that the flickering triggers the brightness to go down a couple of notches so I have to press the brightness key to put it back up again.

I've also just noticed it could be the power lead causing the problem. When it is not plugged in there doesn't seem to be a problem.

Hmm maybe it's your battery. Take out the battery and plug the power cord in see what happens. Also maybe you need to clean your comp. Research Onyx software. You canalways make a appointment at Apples genius bar at the apple store. Take your comp to a retail store..It's free!! Apple Retail Store - Genius Bar