Safe Mode puts your tablet in a diagnostic state (returned to default settings) so you can determine if a third-party app is causing your device to freeze/reset / run slow.
An alternate method is available if the device can be powered on and is responsive.
With the device powered off, press and hold the Power/Lock button until the Ellipsis screen appears then release.
When the Verizon screen appears, press and hold the Volume up button (second button from the top; on the right edge).
Continue to hold the Volume up button until Safe mode appears in the lower-left of the unlock or home screen then release. This may take up to 45 seconds.