Question : Problem: New PSU - computer won't switch on

I've bought a new PSU. I've installed PSUs before and I thought that I had connected everything correctly. But I get no juice when I try to switch the computer on. So, clearly, I've missed a connection somewhere. Here's what I have connected:

The mains connector on the motherboard, along with the little 4-pin connector that sits alongside it.

CPU1 connector. The power supply has a cable for CPU2, but I don't have an equivalent 'socket'.

Power connectors for my 2 optical drives.

Power connectors for my 3 SATA hard drives.

Power connector for nVIDIA 7900GS graphics card.

Both case fans are connected.

During installation, I accidentally unplugged the power switch lead that runs from 'f_panel' on the motherboard to the power button at the front of the case. I re-attached that lead, following page 28 of my motherboard manual (Gigabyte K8N-SLI), which can be found at - http://www.gigabyte.eu/Support/Motherboard/Manual_Model.aspx?ProductID=1928

I've tried reversing the facing of the power switch connector on the motherboard, in case the polarity was wrong, but I still can't switch on the computer on. Nothing on my computer lights or spins up, even briefly. I know that power is running from the mains through the 'kettle lead' because I can hear a faint hum when I flip the power switch at the back of the case.

Worse still, I tried re-hooking up my old PSU in the same manner. I still can't switch the computer on. This implies that the fault lies not with a PSU, but with my technique of wiring up the PSU. What am I doing wrong?

I've also tried cutting back on how many devices are connected. Currently, no optical drives and only 1 hard drive is connected to the motherboard or the PSU. Still no juice.

Answer : Problem: New PSU - computer won't switch on

In the end, I took it to a computer repair shop. The motherboard has been shorted out by the 4-pin mains connector slipping out of its header. Oh well.

Thanks for all your collective help.