Hard resetting / factory resetting your phone will solve the following issues:
1. If you forgot your pattern lock
2. If you forgot your gmail account
3. If you forgot your password
4. Apps that automatically force closing
5. Stuck in Logo (sometimes does not work if the firmware is totally damage)
NOTE: Performing hard reset will erase your data.
To hard reset:
1. Turn off your phone.
2. Press and Hold VOLUME UP + POWER Button and then wait for it to power up and to display an Android Robot with exclamation mark.
3. Press the HOME button to activate android system recovery
4. Select wipe / factory reset, press Volume rocker to navigate and press the MENU capacitive touch (left of HOME capacitive touch) to confirm your selection
5. Reboot your phone.
If performing hard reset did not succeed, you need to wipe the cache first in the android system recovery before performing wipe / factory reset.
I hope this tutorial helps you.. If you have any question just drop a comment.