Samsung SGH-a517 turning on

My phone used to only turn on when you press and hold the end call button. But now it turns on with the slightest tap of that button, and it will randomly turn off when I dont tell it to. I have 2/3 battery left and that shouldn't be the problem.

It only started happening lately, and the only thing different from usual is that I rarely have service now, because I am in the rainforest. The other day it was in the sun and a little bit of condensation appeared on the screen. Could this be whats making it weird? Its a new phone, only about 6 months old.

Any suggestions? Thanks!