It will really depend on if you are actually doing the "Hard Reset" correctly. I am including those instructions below. Should it not work, and not let you reset the device, then there may be a hardware issue. This would require the tablet be looked at by a tech to resolve. Unless the tablet was perhaps rooted, then a "Hard Reset" won't work on it unless you unroot it.
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...