The motherboard often has a lock for the video card to keep it anchored. Make sure the lock is, well, locked. Either that or have your case orientated so that the video card would "fall" into the slot from gravity acting on it. A heavy card would be influenced by gravity more so this should help. It might not look worthy and it's not decent for using CD's with.

"You level up the fastest and easiest if you do things at your own level and no higher or lower" - useful tip My 2D game - release on Jun 13th; My tutorials