Samsung Tab GT-P5100 stuck in bootloop PLS HELP MEE!! I was playing with my tab and all of a sudden it started rebooting itself every minute. after that there was this screen asking me to download a custom OS. i don't want to, so i pressed volume down button (it says there to press volume down to cancel. volume up to continue). but i was shocked when it started to download. there was odin which i don't know what it means and says that 'downloading.. do not turn off target!!' so i was too scared to do anything so i just waited for it to finish but sadly it took very very long and i just let the battery drain. when it finally shut down i charged my tab and tried rebooting it. but unfortunately it just stuck in bootloop :(
Seems like you inadvertently booted in Download mode (You held volume down while powering up your device). 
You should've just cancelled the process and everything would be fine. 

Okay now you are on a bootloop, you can try booting in recovery mode (Holding volume up then briefly pressing on power button). 

From there just perform a factory reset and your device should boot normally. Only a con: data loss.