Z axis suddenly stopped going up

This is very weird and I'm a bit upset...

I've had many successful prints with my davinci 1.0, last print was no exception, today, I turn my printer on, and hear a weird noise when it starts printing after pre-heating...
To my surprise, printing bed was at the bottom and the machine was still trying to lower it!
I immediately cut the power and then tried moving Z-axis manually using jog mode, the axis will move only downwards, but not upwards.

Has anyone had this problem before? What could it be?
Thank you in advance!