You say you have the atmega chip programmed already?
You have looked the board over well, made sure there no shorts anywhere, all the connections between components are there?
I would take the chip out, measure between +Vin and Gnd, make sure nothing is shorted.
Same for +5 & Gnd. If that looks good, plug in the power. Measure 5V again, confirm its 5V.
Then remove power & put in your chip. Power it up. The Power LED should come on, and possibly the LED on pin 13 will flash periodically also (all the new boards I have purchased have done that). If that is all working, then you could try connecting to your PC and downloading a simple sketch, assuming you have the arduino stuff all loaded on your PC.