Probably a failed or failing cable. Depending upon how technical you are, you could either buy a new cable harness or splice in a new length.

There is a known issue on all these family of printers where the wires are secured onto the extruder carriage. It concentrates all the bending into a small area and I think this is the problem you are having.

You may well find that eventually the heating and thermister wiring will fail at the same point as well.

Once you get it going, there is a fix here: http://www.thingiverse.com/thing:1549265 that you can print.