Hi, this never happens with me. MacBook pro OS 10.6.4 If the serial monitor window is open then you get a disconnect dialogue box but that's about it. I regularly unplug the USB when making changes to my circuit boards.
1) Use the # key when posting 2) Ask a sensible question 3) Check you have selected the correct serial port and board type from the menu. 4) Remember that the code you are trying to down load is irrelevant if it won't download.
It is difficult to match up that schematic with that photo. It is not clear what happens to the negative terminals, the schematic suggests you have the diode across the coil, if so where are the negative terminals going? Or is the circuit doing more than just switching the solenoids?
If your schematic is hard to follow what makes you think a photograph is any easier? You have clearly done something wrong either in design or execution. If you want the best help we need to see the schematic first to see if it is designed right. Then we need a photo to see if you have implemented the design correctly.
Then I unbridged some traces that looked like it was straight from the +5v reg to a ground.
That in itself would not be an issue.
However there are two ground and two Vcc pins. If you get one of the grounds shorted to the Vcc and the other not, then that could blow things. Also if you fry pins 0 or 1 then it won't download with the boot loader. The easiest way to fry a pin is to connect it to +5V, set it to an output and then write a zero to it.