When you struggle to connect to a modem please ensure that the newest modem firmware is installed.
If you have flash manager you can use YAT to update the modem firmware.
Steps:

1. Ensure that your modem's port framing is 8,N,1
   
2. Type !9 SERIAL in the command mode
   
3. The unit will then restart in boot mode
   
4. Click on the firmware button in YAT and brows to the attached file an click to open.