Hi. Assuming you have tried several SIM cards with no success. I will need you to take a close look into the SIM slot in question and see if you can see all the 6 gold metal heads - check if any looks bent or broken. Unfortunately, the SIM chip on the motherboard tend fail without necessarily a fault on the user's part. If you can still see all the metal goldish heads, then you can return the tablet to your retailer (CNA/Edgars) for a free service or replacement under a failed-in-warranty.