I don't see any problem with your connection so it must be your program
or you have done something previously to damage either the AVR pin or the transistor.
Disconnect the base resistor from the AVR, the 10K pull down will hold the transistor in off state,
then connect the !K input resistor to 12v, it should turn on.
You can either try with another pin or connected a led to the pin of the AVR
using a resistor about 330ohm for 5v,
then see if the led turns on/off.
Alex