First thing to do is check for shorts. Use a multimeter and check resistance across the power inputs and from any 5V pin to ground. Both measurements should be in the kilo Ohm range or higher. Then before inserting ATMega or Pololu drivers you could check the 5V regulator. Just power up and make sure you are getting 5V where you should.
Once the smoke tests are done, you could plug in ATMega and check for connectivity with Arduino by just trying to upload a simple sketch.
Once the smoke tests are done, you could plug in ATMega and check for connectivity with Arduino by just trying to upload a simple sketch.
