Well in that case it could be a loose GPU. You will have to take off the side of the case, ground yourself by touching a bare metal part while the unit is still plugged in but the power turned off. Take out the screws holding the GPU into the Chassis, reach under the card and depress the retention tab, pull up gently and remove the card. Now just go ahead and press it back into the slot (firmly) and close everything back up. See if that helps.