Heat bed will not heat

[Darshon]

My heatbed suddenly stopped working. I bought a new one and installed it and it does not work either. I do not see anything obvious and have checked all wires. I was going to try to flash firmware again just to try it, but I cannot figure out how to do that either. Please help me get the heat bed working. The extruder heats, but not the bed. the power supply does not even try to turn on so it can heat the bed, but works fine with the extruders. gt2560 i3 pro c

[Mark]

check this link here first:
http://www.geeetech.com/forum/viewtopic ... 13&t=17039