Well considering I just had a very similar problem....
-Check for POST errors (unplug everything but ram and CPU and take out ram and boot, repeat with VGA etc. see if you get the correct beep codes or sound file )
If you pull out a component you want
an error for that component
- If you dont get an error for that component check with the mobo manufacturer and tell them your observations. They should be able to tell you what component they suspect is bad.
- Swap the ram around 1 stick at a time in each primary of your paired slots and also can put dual sticks in on opposite slots
- Swap in a PSU (if you have an extra) and see if it that is the problem
I have to say though given that I've just had this problem with near identical symptoms and had it before with similar symptoms I'd check your ram.
Also for a neat Flow-Chart on diagnostic procedures check out this link