Call 800-922-0204 and speak to customer service or tech support. Make the call from a different phone or land line.
Or stop into a Verizon Wireless Corporate store and see if they can assist. May be a bad sim. Take sim card out and wait a few minutes, then put it back in and see if the device works again. (of course turn phone off first) Do not touch the metal contact on the sim card. Insert it properly back in the slot, close the sim door and then start it back up.