I know this isn't a PC forum, but I'm at a loss and there are some pretty good minds on this forum. This is a PC hardware question for a Dell XPS400. I shut the pc down normally and unplugged it from the wall. When I plugged it in again it would not start. Nothing. No power light, no diagnostic lights. NADA, ZIP, ZERO. verified it was getting AC power to the supply. the front panel power switch is OK. I checked continuity at the motherboard end of the front panel ribbon cable and there is a good switch closure. The power supply checks out OK. I removed the main power connector from the motherboard and grounded the PS-ON signal and measured all the supply lines. All were healthy including the PS-OK signal. I removed the PS-ON line from the connector and plugged the connector back in to the motherboard. I grounded the PS-ON line to see if I could get it to boot. The power supply came on, the diagnostic lights went through their sequence and the diagnostic and power lights went off but the hard drive light stayed on solid. I monitored the PS-OK line and it remained at 5Vdc (PC OK condition). Do any of you guys out there know anything about the power control logic on Dell machines?