XMS I saw your P5B stopped posting, no beeps, no sign of life. I've had this happen to me before.
What you do is shut off the PSU, and clear the CMOS. Then proceed to remove the video card, sound card, and memory. Once you have those things removed, fire up the rig. It should beep a few times. Hold the power button to shut it down, and turn off the PSU. Re-install the video card and ram. Tada, life