Disconnect the 'pc' wires so it's no longer part of the circuit, take a volt meter, positive lead to +3 (or 5) that you are running the Ardunio from... Take the negative lead and connect it to the Collector of the transistor...
Now toggle the Base of the transistor high/low with the Arduino and confirm the volt meter jumps from 0 to +3...
If not take the positive lead of the volt meter and attach it to the Base of the transistor, and the negative lead to ground... Now toggle the base high/low with the Arduino to confirm the base is in fact getting toggled...