No if it was broken his machine wouldn't be turning on at all.
You sure you haven't changed any graphic settings on your client?? I can't imagine what would cause such a drop besides a driver change, hardware change, and settings turned up. I have rarely seen viruses cause such issues but I suppose it could happen.
First lets look for a rootkit. Download TDSS Killer and before you run scan go to 'Change Parameters' and check 'Detect TDLFS file system'. Click on okay and then run scan. If it does find TWO items.. DO NOT DELETE THEM BOTH AT THE SAME TIME! I can't stress this enough. You can totally kill your partition table if you improperly remove a TDLFS file system. If it finds something please post a screen shot here and show me what it finds BEFORE removing anything.