I've checked and double checked everything on it.
The power supply is operational - the motherboard power light glows.
But on pressing Power, the light in the button doesn't come on, and no signal is displayed on the monitor. The HDD light comes on for 30 or so seconds.
The diagnostic LEDs on the back (the A B C D lights) aren't on, and my reference doesn't help me.
Power supply... checked.Make sure that the computer is connected to a known working electrical outlet, and then check whether the front-panel power light is on or off. If the power light is off, check the power supply. If the problem persists, see "Contacting Dell" in the Solutions Guide for instructions on obtaining technical assistance.
Remove all cards. If the computer still does not start, see "Contacting Dell" in the Solutions Guide for instructions on obtaining technical assistance.
And I'm out of warranty by give or take 4 years, so seeing the "Contacting Dell" section in the Solutions Guide won't help me... and besides, who wants to waste 5 hours on the phone with an outsourced tech?