Help! Computer won't boot

[spib]

I came to use my pc this morning but it was switched off (was running when I went to bed) and when I press the power button it won't boot. The led on the motherboard is on and my phone is charging via usb so I know it's getting power. However, when I press the power button, the fans all move very slightly and a red led on the montherboard comes on but that's it.

Is it my motherboard or PSU which is at fault here?

PSU: Tagan TG420-UO1 (420W)
Mobo: Abit IC7

Cheers

 

[spib]

Thanks for the reply. I've been away all weekend so I've only just been able to look at this. I tried a different PSU today (crap QTEC 400W) and the PC wouldn't boot with that either. I also tried the Tagan PSU with another PC and it worked fine. This suggests my mobo is dead right? Is there a way to find out what the light on the mobo means? I couldn't find anything in the manual

 

[spib]

I've tried booting it with nothing plugged into it except the cpu, fan and case switches and you can hear what sounds like the fan trying to spin but nothing happens. If I hold the power button in this continues but If I release it, it just turns off again