I just built a new pc, threw in a Gigabyte MA790X-DS4 moboard with a AMD x4 2.2ghz, 2 GeForce 9500gt's, with 4gig of RAM, and 2 500gb hard drives.  All being run by a 900w modular power supply.  When I plug it in, the green led on the power supply lights up, and when I press the power switch, I get a momentary blink on the led's on the fan.  The cpu fan doesn't turn, nor do any of the other fans.  I get no beeps or anything.  This is like my 7th pc which I have put together and the 1st one that I have had a problem with.
Before I take it somewhere to get it looked at I wanted to see if anyone had any ideas.
I am sure it's something stupid and simple.
thanks