Tab 2 10.1 P5100 stuck on starting screen
One of first links in google. Try it.

http://www.tips4tab.com/how-to-restore-galaxy-tab-2-10-1-p5113-to-stock-android-4-0-4-ice-cream-sandwich-with-official-firmware-ueblh3/

In short:

You need to download Odin and firmware package. You boot to download mode, open odin on computer and connect your tablet to pc. You select the frimware donlowaded earlier and click start.

If something fails then you can do again power+volume up.