Ok so something happened and now your device will not boot properly. It doesn’t really matter what you did or what happened but as long as the device will still turn on [in some way at least] and you can get to download mode then you should be able to recover it and get it working again.
There are 2 things you can try. The first is to flash a stock firmware image back to the device. This will fix such things as flashing an incorrect boot image or if something in your system has been corrupted. The second is to perform a wipe data/factory reset in your stock recovery screen. This will format the userdata partition [wiping installed apps and internal sdcard data] and put the device back to its ‘out of the box’ state. If you downgraded your rom and ended up in a boot loop or made changes to your system settings and now your device will not boot then a factory reset should fix it.
So let’s get going already..
FLASHING A STOCK FIRMWARE IMAGE IN DOWNLOAD MODE
1. Firstly you need a stock firmware image to flash back to the device so go to samsung-updates.com and select your model from the drop down list. It is IMPORTANT to make sure the image you download is made for your model. After you select your device, click the ‘download’ link of the version you want to download. This will be in a zip format but the file you need to flash is inside.
Note: You can also try Sam Firmware Downloader from *HERE* to download the latest firmware for your device at a much faster speed than file sharing sites.
2. You can either use the Toolkit to extract the .tar.md5 image for flashing [option 10,4,2] or use a compression program such as winzip/7zip to extract it.
3. Reboot your device to download mode. You can do this on Samsung devices by holding the volume down, home and power buttons all together for about 10-15 seconds until you see a warning screen. Press volume up to continue.
4. Start Odin from the Toolkit folder and connect your usb cable if you haven’t done so already. Click on the PDA tab and select the .tar.md5 file you want to flash. A checksum will be made to verify the file is correct.
5. Make sure ‘Auto Reboot’ and ‘F. Reset Time’ are ticked and nothing else.
6. Click on ‘Start’ to flash the firmware to your device. The partitions will be flashed and when completed you will get a message at the top left saying PASS.
7. The device will reboot after the flash and should boot up properly. If it gets stuck after the Samsung logo or goes into a boot loop then you need to wipe the device which is explained next.
PERFORMING A FACTORY RESET IN STOCK RECOVERY
1. Reboot your device to recovery mode. Make sure the usb cable is unplugged and hold the volume up, home and power buttons all together for about 10 seconds until you see the samsung logo. Let go and the stock recovery will load up.
2. Press the volume down button to scroll to ‘wipe data/factory reset’ and press the power button to select it.
3. Press the volume down button to scroll to ‘Yes’ and select it [power button].
4. After the wipe completes select ‘reboot system now’ to reboot your device.