I just reviewed your thread on the "packard 820" case. I the same problem with a HP XT933 system. No boot, No posts, and no beeps. Unable to get to BIOS. The system P/S has a green light indicate. No other obvious symptoms. I've systematically disconnected all devices, swapped Ram chips and replaced cables.
I've had the same problem from a brand new M/B I placed on another barebone system. Is this becoming a plague or what.
Any advice will be greatly appreciated.