So, my MacBook Pro 15" has been running slow lately with the wheel spinning at random times. I've owned it for about 3 years and lately I've been pushing it a little hard with Uni work - multiple preview and word documents open, iTunes and chrome open, nothing I thought a normal mac couldn't take. However I was on Skype this evening and the pages started flashing, flickering and kind of overlapping each other. This happened for about 60 seconds until the screen was a mess. I decided to turn it off manually, and since then I've not been able to turn it back on. It appears to be charging fine and all the lights on the side show up. Can anyone give me any pointers and if a repair is necessary how much I am expected to pay for it? Many thanks.