No USB Modem Not Showing in Serial Port

Hi,

Sometimes when I plug in my Arduino to the USB port, there's no USB Modem option showing in the Serial Port. I thought maybe the USB port is driving too much power and disabled. But after plugging it again or restarting my laptop, it still doesn't show the USB Modem. Then randomly, it will show up again. What might be the problem?

Thank you!

Could be a bad cable, bad connector on the Arduino, or bad USB port on the PC.