Can't get anything to power up

[whookid36]

Hello I just recently put together my build.
AMD Phenom II 920 2.8ghz
Samsung 1tb hard drive.
Gigabyte MA790GP-UD4H Motherboard
650w Top Power power supply.
2x 2gb ddr2 kingston
ATI Radeon 4850
Coolermaster 690

All the standoffs are in. Tried using one memory stick still wouldn't post. The only thing wants to run is the power supply fan.
I got the 24 pin and 8 pin connected. Cleared the cmos. I'm not sure what to do this is my first build.

 

[The_Prophecy]

Woot! 2000th post! Now to my suggestion...

Made sure everything is plugged in? Those 6 pin PCI-E connectors on video cards render systems completely unbootable and useless (often with little or no audible warning) if not plugged in.