Have you downloaded the latest drivers from HP, then tried to update your driver manually? Control Panel-> System-> Hardware-> Device Manager -> click on USB settings if the scanner isn't listed, and see if you have unknown device. Then right click on the device and "update driver".
Sometimes plugging into a different USB port will cause the device to be re-detected. Sometimes a reboot without the device plugged in then another reboot and plug the device in. Usually this can "jump start" the detection of the device. Sometimes you have to search and clean the registry, and start from scratch.