Geeetech

I received and built a prusa i3 x about 3 weeks ago. From day one the heat bed would not work though the thermister does. I have double and triple checked the plugs to make sure they were in their proper locations and they were in tight. After looking at a few posts here and looking at the board I see that the led light under the power socket is not lit when the bed is programed to heat up

so you can check the heatbed mosfet that controls the heating, see if it is dead or not, check out this link:
http://www.geeetech.com/forum/viewtopic ... 19&t=17039

with the power on and the heat bed programed to heat up the voltage across pins 2 and of the mosfet is 0.0

yes when heated up the heatbed the voltage between pin 2 and pin3 is 0V, that correct. So when not heated up, did you get 12V? If not I think you need to check the PSU output for the bed, is it 12V?