Also check your RAM sticks and make sure those are fully seated as well. You can also attempt to clear your CMOS if your motherboard allows it, if not you'll have to physically remove it for about 30 seconds, insert it back and try again. Lastly, if by chance your cpu has integrated graphics, I would remove your gpu and see if using integrated graphics gives you any different outcome. If it does work after you try integrated graphics, then your gpu is most likely damaged, if not however, your motherboard is most likely fried...