Many M2M solutions do not have a display installed to show you why your SIM is not in a network.
If you activated the SIM card after your device is turned on you will have to do a hard reset on your modem to force the network attach. Often this is done by switching off all power from the device 1 or 2 minutes.
Try plug the SIM card into a mobile phone to see the status of the network. Remember to change the APN settings on the mobile phone.