It sounds like you are having a power related issue. Power management problems with the USB modem are for one reason or another; do not have the required 500mA to the modem. The USB controller normally shares all the powers with other chipsets onboard. Unfortunately, due to poor drivers, the USB power is cut when either the motherboard cannot provide enough power, or it assumes the modem is out of use and cuts the power to it. Solution to this problem is to use an address on the PCI USB controller card. That way it has its own power.