Arduino uno stk500_recv()

Hi @ all I have 2 identical Arduino Uno boards with atmega328 chip. Yesterday I was installing the arduino into place powered by a 12V source. I pulled out 1 of the wires from a relays to switch them and I shortcutted it. After that the Arduino went mad.

I'm running OSX 10.7. The second arduino uploads every program just fine, the first one does nothing. I've read a lot of problems concerning this message however none of them helped me.

so, 1 with the error stk500_recv() and the second works fine, so the problem lays by the arduino board you can say. Any ideas?

Kind regards, Egbert