What model is it? Is it a surfboard by chance? Is it a USB or ethernet type? If so, you most likely need updated XP drivers:
USB drivers below:
http://www.gi.com/noflash/usb_drivers.asp

Use the above just in case SP1 caused a driver reinstall, that is not working now. SP1 is known to reinstall drivers for XP... usually they are generic or older drivers than what is available.

Another thing you can try is resetting your modem. First disconnect it from the USB or ethernet cable, then get a small pin or toothpick, and find the small reset hole on the back of the modem, (there may be a reset switch or button) push it and hold for 5 seconds. Then power off the modem, (turn power switch off or unplug the power adapater), then plug it back in and try it out.


Just my advice.
BB