Samsung Tab GT-P5100 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.