USB/Ethernet/all ports not working

The USB/Ethernet/all other ports on the back of my iMac have stopped working. I plugged a USB cable in and it touched a lamp with a short--it arced and now the USB and Ethernet don't work. The computer boots seems to work fine, but I can't interact with it via keyboard/mouse/ethernet. The airport is off so I can't try connecting via wifi.

My guess is the bus with the ports has been fried. Is this on the logic board, or is it a separate board that's easier to replace?

In addition, any ideas on how to connect/interact with the computer without the use of USB/Ethernet/Wifi?