What are your system specs? Is this a new build? PSU upgrade? Motherboard upgrade? Please tell us the circumstances that led to this problem.
if this is a new build or included installation of motherboard, a common issue is unused mobo stanchions in the case. Breadboarding is a great place to start for your indications: http://www.tomshardware.co.uk/forum/page-262730_13_0.html
Another good troubleshooting thread: http://www.tomshardware.com/forum/261145-31-perform-steps-posting-post-boot-video-problems