Hello,
There couple be many reasons for this happening, did your battery die during the update? Or are you rooted? Although there are many reasons it could happen there is one solution that should work. Enter download mode if possible but holding power down and the home button at the same time during boot up! Download the stock firmware from sammobile.com and flash it through Odin. If you are not familiar with odin leave a comment and I can help you further! Hope this helps!
:if you found this helpful please vote up the answer and aide to my rep, I will do the same!
Thank you!