I just installed ZenUI launcher and somehow it fixed the problem in my Galaxy S3 Neo. Edit: My phone was able to start but whenever I tried to clear all the open apps by pressing the home button for 2 seconds, it showed this error message ['com.android.systemui has stopped working, unfortunately']. So first I factory reset the phone, the error was gone. Then when google play store was restoring all my apps, the error message came back. After lots of hit and trial, I installed a Launcher and then just by installing (not even using it), the error was gone.