I'm working on another Pavilion (the 750n this time) and when you plug it in, it automatically turns on without the power button, does one solid beep for probably 5 seconds, and turns off, won't let you press the power button to try again. The only way to get it to do the problem over again is to unplug it, and plug it right back in. I started with the power supply, tried it with my own power supply, same problem. I unseated each RAM module, and moved them from each slot to see if it was a slot. I swapped the video card, I unplugged the HDD, floppy, and both optical drives individually, removed the PCI cards, I even took apart an old Compaq I had here and tried a different CPU. All the fans are working. There is nothing displayed on the screen for the 7 or so seconds the computer stays running. Any other suggestions?