I just recapped my AOpen board but after plugging everything in it didnt boot.

When the 12V ATX is unplugged but the other plug is connected to the board the fans all turn on when I power on the box.

When I plug in the 12V ATX connection and power on the box nothing happens except that I hear a small whistle for about a second.

Can anyone give me any suggestions for what is wrong.

I have checked and all the caps are to the correct polarity and seem to be connected firmly to the board.

I only powered on the board for a few...