If you are hearing the fans running loud, then this could be a serious hardware problem. It is sounding like the video card failures on the older macbook pros, but that was limited to models dated 2008 or older.
My first suggestion is if you are close to an apple store, take it there and have them test it, they should not charge you, I have gone in many times and just had them run their diagnostics, theirs is better then what is included when purchased.
If you are not close to an apple store or don't want to go out, run the included diagnostics when you purchased the computer. You can do this by pressing the "d" key on startup. You may have to insert on of the reinstall disks to boot to this, it would be labeled on the disk needed. Newer models that don't include disks, and some that did, do not require a disc installed. But usually it would be installed on the hard drive as long as it is original and has not been wiped.
Once you have gotten the results, post back the results. This will help diagnose the issue a little more. This will so any failures it detects, but if you get a passing result, this could mean that there is an intermittent problem.
