Make sure the drivers for the modem are installed. The PWR light will not illuminate until the drivers are installed. If the drivers are installed, then check the following possible solutions.
Make sure you are using the proper cable. Be sure you are using the USB A to B cable that came with your modem.
Your USB port may not be enabled. To ensure USB is enabled on your system:
Do one of the following:
Windows XP users: Click Windows Start > Control Panel.
Windows 2000 users: Click Windows Start > Settings > Control Panel.
Double-click the System icon.
Next, click the Device Manager tab.
If your USB is enabled, there will be a USB icon and the words “Universal serial bus controller” under the Computer icon. If USB is not enabled, you will need to enable USB in the system's BIOS. For instructions, check with your computer manufacturer's technical support. Once your USB port has been enabled in your system's BIOS, Windows will automatically detect and install USB support when it restarts.
If the modem has worked previously and you removed the USB cable from the computer and then reattached it, try another USB port. It may have been set up originally on the other USB port. You should notice some minimal activity from your computer such as hard disk activity or an hour glass icon for a few seconds when you insert or remove a USB cable from the computer or the USB device. If you do not see anything, your system may not be properly communicating with the USB ports.