Kind of need more info to help troubleshoot this.
Is there any damage to the device?
What was going on when connectivity ceased?
Is there damage to the SIM card?
If it happens all of sudden, then this will be a software issue.
Problem may be of two type :
Software can be repair through Hard Reset, Just try the combination (Power + Volume up + Menu)
and if it fails then you have to Flash the device.
Download files from Samsung-updates.com
and check guide how to flash samsung android tablet
If the software section fails to solve your issue, then you have to Change network ic.
(Use multimeter to check PCB)