Alright another tutorial for Samsung, and this one is for Samsung Galaxy Core (i8262). Sometimes this tutorial does not work because the Android System Recovery is not installed in the system. Its either disabled by the manufacturer or the Carrier.
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 Samsung 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 + Home Button + Power Button simultaneously
3. Release the buttons when you see the Samsung Galaxy Logo Core logo
4. Android System Recovery should appear
5. Select wipe / factory reset, to navigate press the Volume Rocker, to select press the HOME Button
6. Reboot your phone.
Note: 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.