Extruder not heating

First, i am very new to the reprap build process. But i have everything working except for the extruder is not heating. I am using repsnapper for the software, it appears to be confirured correctly, it is sending a line to turn on the heater, but nothing happens. I am using a arduino mega board and i have the extruder heater plugged into the D10 slot. When checking the screws on the D10 when it is on and supposed to be heating, with a multimeter it doesn't read with any volatage. I have double checked all wiring and all is in order. I am at a loss. Any suggestions what i might be doing wrong?

I assume that you have your firmware set to use D10 for the extruder heater and you were measuring the voltage across the + and - terminals. How about when you measure the + terminal versus ground? Do you measure +12 V? Have you measured the voltage with the heater disconnected to make sure you're not shorting it? How about the resistance across the heater lead wires?

Did you measure the voltage on pin 1 of the mosfet vs ground?

Also what temperature is being read by the thermistor?

If you suspect a bad mosfet, you can change the pin assignment for the heater in the firmware to one of the other two: D8 or D9 and see if you see voltage across the +- terminals without connecting your heater.

what version of firmware are you using? also what board are you using? thx

If the Fan output is working, you can temporarily plug your heater there, and check things getting warm. Make sure you check the resistance on your heater too. It could e that you have a short (yes, I know you checked wiring).