SIM Card doesn't work

I have a Dell Venue Pro 11 – 5130. I'm trying to get network connection through a service provider whose SIM card I purchased. I inserted the SIM card in the SIM slot after removing the battery. The tablet does not recognize the SIM card. I have tried 3 different SIMs with no luck.When I go to　

Settings → Change PC settings → Network

no network is listed. Do you know why the SIM cards are not recognized? Does the tablet need to be unlocked?