A reboot is just turning it off and back on, I am going to assume you mean a 'reset' then. If that is the case, you can try the following to do a "Hard Reset" on it, but it will have to be able to turn on during the reset. If it won't then you may have to have the tablet looked at either by the manufacturer if it is under warranty, or a local tech if it isn't.
NOTE: Doing this will clear 'all' the data on your tablet, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the device.
Be sure you back up any data you want to keep, to a computer or cloud account, before doing the reset.
To "Hard Reset" the tablet...
1. Make sure that the tablet is actually powered off.
2. Remove...