Well, it's supposed to happen.
So don't worry. Slip loose from the shackles.
Just press 7 and 9 rapidly.
Attract the guards attention so he'll open the door.
Go really close to the cell door.
He'll enter, and start to beat you up.
Well, fight back you wimp!
After you hit him a couple times, run out.
You can't kill them with your hands.