Help me solve this problem please

I turned my computer on this morning and everything on my monitor looked normal, going through the startup script as usual. Then, the screen went black (not standby, apparantly getting a black signal) and stayed like this for a few minutes. I did a ctrl-alt-delete and got a black screen again.

Next I did a force shutdown and restarted to see the monitor flashing "no signal", but what concerned me is the LED light that normally runs solid (showing the computer is on) was sort of thready and flashing quickly.

Diagnosis???

I first feared that one of the hard drives on the RAID setup was down, but when I disconnected them and connected another hard disk with an operating system installed (and used the jumper settings to make it the master drive), I got the same problem.

Next I thought video card, but the normal beeps associated with a bad video card were not there. Took the video card out to make sure, and no beeps when restarting. I am now fearing mother board failure. Thoughts??

Thanks in advance,

MisterW