I'm experiencing this problem as well. My motherboard was purchased at Frys and I no longer have the receipt etc. The problem is very, very troubling when I'm trying to dual-boot between Linux and Windows. How can I choose the OS when it doesn't even show me the Boot Menu! I tried everything I can think of, simply put the mobo is flawed. Whatever causes this I support my fellow here in saying it's real. Here's what happens:
1. Power-up, system will sometimes boot with monitor signal, other times 1/2 way through Vista loading it works.
2. Resetting the system causes the problem to be abit worse, or rather unpredictable. It's very odd but will seem to have no signal even though I hear the beep, then later it beeps again! So it beeps on reset, then no signal, then later beeps, then monitor signal awhile later. Weird!
You're not alone pal, I don't think BIOS can fix it because it's done this ever since I had it, the thing is just poor quality IMO.