that sux... the button itself migh be an issue..
I cant see how to fix that withought taking the phone apart..
Ive taken a few touch pro 2s apart and the bottons on the front pannle have 3 scrwes, one under the talk, one under the end, and one between the start and back key.
What MIGHT have happened is that the prong under the button that is sapouse to bring the button back up might have been broken..
either that or the soft pad under it might be sunk in.
One or the other would have to be replaced
I sudgest taking it up to the repair center near you and see if they can do anything about it.
if you do it yourself you risk alot of damage to it if you dont know what you are doing