How to Factory reset the Galaxy S3 with stock android recovery.
How to enter Android recovery & Factory reset the Galaxy S3
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Warning... do this at your own risk.
I am happy to help with any problems my subscribers are having on their android devices. I am going to need lots of info from you to help. 1. What device you are on. 2. What android version you are running. 3. What rom or stock rom you are on. 4. What you have done to the device. 5. What recovery system you are using. With this info I will be able to help much faster.