The lights are on but nobody's home: no response after power on

[jbhelfrich]

So I moved my wife's PC to a new case today. This was to accommodate a new video card that was too large for the old case, replace a non-system hard drive, and generally clean things out. In the course of cleaning things out, I opened the power supply, because there was a large amount of dust and cat hair built up inside. I plugged it in and turned it on before I connected it back to any components, no problems.

I plug everything back in. I flip the switch on the power supply. Happy green light on the motherboard. I push the main power button. Everything lights up, no sparks, no magic blue smoke, fans are spinning, everything looks good.

And then nothing. No POST beeps (though I don't think there's a speaker attached). No video signal to the monitors. The keyboard LEDs (it's a Razer) don't turn on. Hitting the reset switch doesn't do anything. Holding in the power button doesn't do anything. To turn it off, I have to flip the master switch on the power supply.

I pull the power, check all the connections, and try again...no change.

Please tell me I'm missing something simple.

The CPU and RAM were never removed from the motherboard,

 

[DSzymborski]

All the specs, please - I don't know the GPU or the PSU or well, anything about the PC, so it's hard to give more than blind speculation.