When you begin to raise the roof that foot high in the back and then it stops because the front is not raising, can you then lift by hand the front and raise it.
If you can, have someone continue cranking the top up and someone else keep lifting the front.
Once it's at full height, lower it.
Then try cranking up again. If not change, then there is probably a gear slipping, or more likely, the teeth are sheered off.
If, on the other hand it raises the second time on its own, then it was just the cable that needed to somehow reseat itself, or rewind itself.
Other than this, I can't think of what else to check, providing none of the cables are broken.
If, you cannot lift the front by hand as someone is cranking the back, it's stuck, then chances are, the cable itself is kinked or tangled, or frayed and tangled into itself in the tubes or gears you can't see.
