: Use the AT command AT+ZMODE=1 to switch the modem to CDC mode and re-enumerate the device.
On Ubuntu/Debian:
Try a different USB port (preferably USB 2.0, as some older dongles struggle with USB 3.0 controllers). Driver Signature Error: On Windows 10 or 11, you may need to temporarily disable Driver Signature Enforcement to install older, unsigned drivers. Flashing Blue Light:
Problem 2: The Modem Only Connects as a Mass Storage/USB Drive