M140 Heating Bed AND Extruder

Hello every body,

I've struggled for a while now with this problem. I decided to upload the latest Marlin firmware and did all the changes. Every thing works fine except heating up the extruder. When I send M104 nothing happens (thermistor is reading correct room temperature). But when I send M140 RAMPS start to heat the bed AND the extruder... So I uploaded the old firmware thinking of a hardware problem, but it works fine with the old firmware. Does somebody have an idea what is the problem?

Thank you

Trachsou