You may well have to pull the battery (yes, I know some are hard to get to) or just wait until it runs out of power and shuts down.
NOTE: If it is under warranty, don't open it up yourself, as that can void the warranty. In that case I would wait until it runs out of power.
You may also want to try turning off any local WiFi (modem/router) or take it to where there is no WiFi connection. Any update issues could cause this as well.
Once you do get it turned off, let it charge for a short while and then start it up in "Safe Mode" so you can run some checks to make sure everything is OK.
How to enter "Safe Mode" when booting the computer.
In Windows 8 and 10...
As your computer restarts, press F8 (possibly a few times) to enter...