Before you remove the PTO, read the mounting instructions.

http://www.phtruck.com/download/training/truck_training_online/pto_training/5_pto-installation.pdf

You need to have the proper backlash. It is not a simple matter of reinstalling it. It is very unusual for the PTO to engage by pushing in the cable. It is usually the other way around. You should be able to get to the PTO to pry it in and out of gear. Depending on how it is mounted, you may have to take the center of the floor board out to get to it. Is it a dump bed or what? Do you know if it ever worked>