Hi. Start off by restarting it and observe. Then try in a differeng SIM and restart the tab again. If the issue still persist, you will then have to return it to your retailer if it is not more than a year old. If you bought it second hand, then it may be that its IMEI number has been blacklisted due to having been report lost or stolen. You will need to contact your seller in this case. Let us know.