Recently ran through a debug of what the OP described as:
"My P5Q is boot looping (it seems) whenever I put a graphics card in. I stripped it down to just cpu, memory and graphics card. Without the graphics card I get a short startup beep followed later by 1 long beep followed by 3 short (no vga), but when I plug it in I get one short startup beep followed later by another short startup beep."
Swapped PSU's, vid cards yielded no change. Eventually, the DVI cable was removed and replaced with a DVI-to-VGA adapter, and the monitor's vga port was used. The PC booted up normally.
Question: What kind of monitor/cable failure caused the original symptoms?