avrdude: verification error and other weird behavior

Hey,

I´ve just received a new hotend and everything went well until I wanted to plug in a cooling fan in the 12V pins.

I'm working on Sanguinololu 1.3a with Marlin or Sprinter. Both firmwares worked before and I managed to heat it up one time, but while fiddling with the 12V pin I must have shorted the them resulting in my computer shutting down. What could I have burned or f**ked up with that?
After I pulled out the fan the board connects normally again but the hotend thermistor show 109C constantly even when I pull the thermistor plug out.

Trying to reupload the firmware (compiles normal) results now in

Quote

For marlin
avrdude: verification error, first mismatch at byte 0x69ea
0x48 != 0x4a
avrdude: verification error; content mismatch

and

Quote

for sprinter
avrdude: verification error, first mismatch at byte 0x0002
0xf1 != 0x1d
avrdude: verification error; content mismatch