Originally Posted by
Briannlim
My mountain bike is stuck at the 8th gear which is the highest . When i try to shift the gear using the shifter, nothing happen to the rear gear at the back. Not a single movement. I tighten the cable by pulling the cable under the rear deraileur. Sorry for not giving enough details because i dont really know about bikes as i am still very young . Thanks for your help guys . Appreciated

You should check the cable housing to see if any of the internal wires of the housing haven't slipped out. They sometimes will slip past the ferrule and jam the internal cable.