Build a PC Problems installing motherboard bundle


TS Rookie

My old PC died so i recently purchased a motherboard bundle to replace the broken parts. I bought the following:-

Motherboard: Asrock N68C-S UCC
RAM: 4GB DDR3 (1333 PC 16660 OCM)
Processor: AMD Athlon II x 4 630 2.8Ghz
Hard Drive: Sata II 500GB

As well as that, I also have a Nvidia 8800GTX graphics card, 400watt power supply...

As far as I know, I've correctly assembled all the parts. But the PC won't boot up. The fan comes on, but that's about it. Any ideas where I can start troubleshooting? I've already tried unplugging, replugging and testing all the seperate parts.