My Screen blacks out!

Hey there, In the past 2 or so weeks my Laptop (acer aspire 5735Z) Has been doing weird stuff. In the right hand bottom corner the corner is blacked out and sometimes the screen goes black but it is still on and if I'm listening to music I can still hear the music, I have to turn the computer off and on to get the screen black. Does anyone know how I can prevent this happening as it is coming up to my Exam's and I don't want it blacking out while I am studying!

Thank you.