OK, I thought you may have just installed it and were missing something in the process. I would shut it down and switch off the the power supply so it can't start back up by accident. Then remove the side panel and touch the power supply with one hand to discharge any static electricity on your body. Now re-seat ( remove and then re-insert) your video card, RAM modules, and any other add-in cards like sound cards and network cards. Check all your data and power cables to make sure non of them are loose. If there is a lot of dust inside you may want to clean that out. You can buy small cans of compressed air at Staples, Futureshop, etc for that. You can do it with a vacuum cleaner too if you are car full. Now leave the side panel off and power it up. Check to make sure all the cooling fans are working. Specifically the one on your video card and the one on your CPU heat sink.
EDIT: If there warranty stickers preventing you from opening the case without breaking them, make the call before doing what I suggested above.