Reboot to bootloader (hold down power for approx 10-15secs and when screen shuts off hold down the vol down button also). Use volume keys to select "recovery" press power button to select recovery. When in recovery, select wipe cache and then reboot. If this doesn't work, you might need a factory reset, which will clear data partition. All apps, texts, etc will be reset to factory defaults and should be like almost just out of box condition.
Edit: to back up your data while not being rooted, look up PC apps like "Mobile Go" to back everything up to your PC.
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