i access internet through a usb modem on both my laptop and desktop, but recently ive been unable to connect via my desktop. ive used the same usb modem successfully on 2 desktops identical to mine so im not sure why it wont work on this particular one. ive used a usb modem from a different isp and it has worked fine. my OS is Win 7 Ultimate. what else can i try to identify the problem