Hi,
First try to factory reset your device (this will erase all your personal data!).
1. Hold down the power button to switch off the device.
2. Press and hold the Volume down and the Power buttons.
3. When the phone entered the Android System Recovery menu release the buttons.
4. Use the volume Up and Volume Down buttons and the Power button and select:
wipe data/factory reset, Yes--delete all data, reset device
If this not help you you have a hardware problem, most likely touch screen problem and you need a replacement.