System cannot detect modem and modem LED is not blinking. What should I do?

When modem LED is not blinking it is either PIN numberis present or SIM is not working/ activated.
Do the following check:

• Remove SIM and modem from USB/modem
• Put SIM into normal phone
• Make sure there is no PIN. If there is PIN, remove PINand set phone to disable PIN
• Try to make a call or send SMS with SIM in the phone