I suggest doing a soft reset first. Occasionally, the software glitches out and does not register touch screen input, but it does register fysical button presses (on the side of the phone). Just hold down the power and volume down buttons for about 10 seconds till the phone reboots. This cleares cache but also resets the time. Don't forget to set time. If this doesn't work, you will either need a hard reset, reinstalment of the software via a computer or just total replacement. NOTE: A soft reset (power button + volume down) does not delete any files or data, a hard reset (=cold boot), however, will.