Hi guys - I thought my technical knowledge was enough to build a computer - but apparantly not.....

I believe that all the hardware is connected properly, but the machine doesn't boot at all. The light comes on on the motherboard, but no clicking, whirring, spinning or anything at all - what sort of obvious things should I look for? (I'm pretty sure that the System Panel Connectors are correct)

400w Power
A8N-SLI motherboard
Athlon 64 3000+ processor
geforce 6600 gfx card
80gig hdd
dvd rw
standard sound card

Hi Squizz,
sounds like there's something wrong, I think the cable which connects the power button to the motherboard is inserted/connected the wrong way, because when your hardware setup is wrong you'll start hearing fans running when you press the powerbutton. Now your mobo seems to get power (hence the green led) but youc annot start the computer.
Good luck, Bram

I've rechecked the System Panel Connectors that connect the case to the motherboard. Is there anything else that I should specifically check? It's still not working....

To me it sounds like a pwoer problem. And sicne the motherboard is powered, the green led, there should be soemthing wrong in the wiring to the power button.
Do you notice anything happening when you rpess the pwoer-on button? A click (from your psu), a smell, a whizz?
Have you also taken a look here? Apparently you need a real heavy psu to get this one going. Have you also tried starting with only the minimum required hardware to boot, connected? (ram, videocard, 1 hd, cpu)?

What Kind of Power Supply do you have? It is a 20 pin or 20 +4 pin? And is it a name Brand such as Antec Enermax. As btalman said SLI needs some good watt's to run. An Antec 12 rail would be enough and other major manufactures with only 400 watts. But some of the Generic ones wont push enough current through psu to run everything.

I had a look at that page, and mine is classed as a light load isn't it? a 400W power supply should suffice. There is absolutley no activity whatsoever when I press the power button......

I also tried the minimum, but it still wouldn't boot.

Mercury KOB P4 400 Watts
Switching Power Supply

• Total output power: 400W continuous maximum
• Built-in long life, ball-bearing cooling fan
• Built-in EMI filter
• Low ripple noise
• Product suitable for P4 Mainboard
• Active PFC/ Passive PFC (Optional)

Is that enough do you think?