First build i3 setup issues

I've just finished assembling my first reprap (i3 kit from 3dprinter czar) , I have the printer set up and roughly calibrated. I can move all the axis and heat the hot end and the bed, all of the end stops seem to be working when I home each of the axis. The trouble I'm having Is when i try to start a print the z axis finds its home before it moves up slightly and then lowers the hot end into the bed (apparently ignoring the end stop). I've tried printing using Pronterface and Repetier and have the same issue. I dont know where to start resolving this, could it be a problem with the config file? ps I'm using ramps 1.4 Thanks for your help.

edit: This video demonstrates the problem. i first home all 3 axis then begin a print. just before the print begins the bolts fall out of the x motor mount on the threaded rod, because the z motors are trying to go lower than the endstop...
[www.youtube.com]

Edited 1 time(s). Last edit at 11/17/2014 05:38PM by fisher.

Hello if you are using slic3r check your start g-code under the printer settings tab. If you see G1 Z5 F5000. Delete this line. I had the same problem with the hot ignoring the limit switch when I tried to print. I hope this solves your problem

Thanks, i'll check that

Just tried that, the line was there under custom gcode in slic3r, i deleted it and reexported but the problem continues :/

Edited 1 time(s). Last edit at 11/17/2014 05:57PM by fisher.

Check to make sure your ABL Is not enabled in configuration h. if using Marlin . You may need to comment it out.