I recently got a new GPU, a Gigabyte Radeon HD 7870 OC Windforce 2GB. I put it into my computer and screwed in the screws. When I turn the computer on, it won't start up. The fans are completely still, and the computer makes does some signal noise. After a little while the computer turns itself off, and a littler later it starts up again.
I have never installed any parts in a computer myself before, so I'm new at this.