Z-axis suddenly only moves down

Hi guys, while printing a part this morning, the print nozzle started at correct height, but when moving from the starting point to the first line, the nozzle lowered and dug into the print bed.

I was reprinting the same part as yesterday, from SD-card so it's the same correct file. There is only one file on the card.

Tried to move the Z-axis from sdramps while lifting the carriage so the endstop is free, but the Z-motors only want to move down.

Anything that can cause this? When I press the Z-endstop while moving the motors down they stop as expected.
Setup is Ramps on a MendelMax 1.5

Is it possible that somehow after months of perfect service, the Marlin configuration damages? I can not imagine this being the case. But when I get back home later today, I will try to reload the firmware as I have the hunch that is might have gotten damaged.

Edited 1 time(s). Last edit at 04/12/2014 04:34AM by Ohmarinus.

Does it home as it should when you press the Z home button?

---

_______________________________________
Waitaki 3D Printer

I think there might be a cable break in the wire or wear in the endstop. After wiggling every part of the cable, it works correctly again. This is bothering me. I will replace them a.s.a.p.

Maybe a good moment to start playing with these magnetic (HAL?) endstops or some optical ones. However, the optical endstops I have at home have not given me continuous results.