I've had this system working great about 6 months. All of a sudden yesterday, no video and no beeps (everything else appears normal: all fans spinning, hard drives working).
I tried alternate output (same graphics card), no good. I switched graphics card, it booted fine. An hour later, it shut down (rather than just going to sleep, which was a first) and the same problem: no video, no beeps.
There's no integrated graphics ports on the mobo to try. I took out the graphics card, and put it back in (making sure it was completely in and secure). No video, no beeps. I took the graphics card out, and put the original back in. Booted great! A few hours later, the computer shut down (again, without being told to), and the mystery reappeared.
It seems 1 out of every 4+ times that I remove and reinsert the graphics card, I can get a successful POST and boot, but it doesn't take long for the computer to shut down and the problem is back. SmartDoctor says my graphics card has no problems.
CPU: AMD FX 4100 Black Edition
Mobo: ASROCK 970DE3/U3S3
RAM: Corsair XMS3 8GB DDR3-1600 (PC3-12800) CL9 Dual Channel Kit (2x4GB)
PSU: Inland Gold Series ILG-400-2 400 Watt ATX
Graphics Card (Original): AMD Radeon HD 5450 512MB DDR3 PCIe 2.1 x16
Primary Hard Drive: OCZ Agility 3 120GB SSD
Secondary: Seagate Barracuda 1.5TB
OS: Windows 7
All parts were new when I put the system together in June 2012. Have had no problems until now.