After you upgrade to Windows 8, you might have some trouble regarding connecting your 3G modem.These are some troubles that can occurs,
- Windows 8 not recognizes your 3G modem drivers when you connect the device.
- Windows 8 taking you 3G modem drivers correctly but after few minutes it will disconnect(device will automatically disconnected).
I assume that your 3G modem worked in previous windows versions (Windows 7/Vista/XP).
So the solution is download the latest mobile partner.