Did I accidentally short something? My Arduino UNO board does not communicate with the computer anymore I had my sketch uplaoded and everything was working fine when I tried connecting one of the input pins(pre-configured as digital INPUT) to 12V, just to see if this was being read as a HIGH as well.
It seems to have done something and the board stopped working. Moreover, all pins seem to be stuck at HIGH! 

So far Ive tried the following:


reset button: doesnt help
re-upload: doesn't work - it says not in sync


Physically nothing seems to be burnt/blown. What am I missing? Have I fried my board? I hope not. PS: It was connected to a 12V external power source

Any thoughts?
Unfortunately, the arduino's input pins are not tolerant of 12 volts, You have likely caused permanent damage to the chip =(. There is a regulator that makes it capable of being powered by 12 volts, but the input pins are different.

If you look at table 30-1 on the datasheet for the Uno's controller here you can see the input characteristics. The arduino is powered at 5v, so the max digital input voltage is 5.5v