ABS print stopped in the middle!>*#? HELP

Hi, I'm using the original Prusa with ABS filament . As you see in the picture it's a big print but it messed up in the middle and i stopped it. what do you think is the problem?

note: cooling fan was off.

Hard to tell from the picture. You don't have a webcam with a timelapse movie of the print, I assume?
My best guess, happened to me once: ABS tends to bend up in corners when cooling during the print, so probably one part of the printed object moved up a little bit, the print head touched it during the print, object got partially broken/hit by the head, and that's the result.

Hard to tell indeed. This is my version.
I see lots of loose strands. The first cm all was ok then parts got bumped off.
So my guess : layerheight to high(in combination with curled corners)