I don't think you're looking at the right thing.
There is a white cable in the boot, in the middle of the panel at the back of the boot, this is the release for the storage compartment (in the cabin) in the event of an electrical failure. This does hang loose.
The roof release is a red handle located at the top at the top left of the boot opening. You pull this out to disengage the roof motor, there is some resistance to the cable and you need to secure it - it will not hang loose. Once the red handle is out you can freely more the up and down. Putting it back re-engages the roof motor. If you haven't pulled the handle out the roof will be very difficult to move as you are pushing against the roof motor / hydraulics. Which I think is what you're doing. You could damage the hydraulics if you are.
The roof motor is located next to the rear of the passenger door, if that's working you should be able to hear it turning when the roof button is pushed.
It's all in the manual - if you don't have one to hand there is a link in my signature to them... there should be some pictures too to explain the above better.