One of two things. The phone might need to be reset OR it simply needs a new LCD.
First try a SOFT RESET. You will not lose data.
1 -Press the power button for about 10 – 15 seconds. > Release the power button when the phone shuts down and reboots.
2 - If that doesn't work, try to remove and replace the battery
Second, if you are willing to lose data or know you have backed it up, try a HARD RESET.
1 -Turn off your phone completely. (Press the power button for few seconds and tab on Power Off)
2 -Press and Hold Home + Volume Up + Power keys together at the same time about 10 seconds.
3 -As soon as you get into the Android system recovery mode, Navigate to wipe data/factory reset using the volume down button and select it with the power button.
4 -It will ask you to confirm “Confirm wipe of all user data?”. Select Yes – delete all user data
5 -Now select reboot system now.
Now, for the screen replacement, there are no guides on here. I'm sorry. But doing some research though, I did manage to find the part you need, the tools, and a guide.