Hook it up to an external monitor. If you get a bad picture then Brain is probably correct. To be sure you have the Nvidia processor please give us the last three figures of your serial number. If you are not close to an Apple store, the Nvidia issue can be handled in four days (start to finish) over the phone.
I would check with your local apple store, there is a recall for the nvidia graphics chipset for this model MBP...... they run a simple test and if applicable your logicboard would be replaced under recall...... i would recommmed an apple store as i have had the best results in correctly diagnosing this problem and having it fixed under the recall quickly.
If it is not a graphics chip issue can trouble shoot from there if the apple store tech don't just go ahead and tell you what the problem is.