the grafs card might be on its way out. If u have a spare monitor, or access to a spare, u could try plugging that in as one test. Another thing might be to check the card hasn't become unseated in the base unit, but if u've never had the cover off, or dropped the machine, this is unlikely. One other thing might be to check that the lead connection is good, and not come loose. Failing any of these checks, it's looking like a new grafs card might be needed.