The first thing you need to do is to go through your TCP/IP settings with a fine tooth comb to make sure they are correct & spot on. Secondly go through all the USB modem settings to check those too.
This might be as simple as a dirty or corrupt DNS Cache or ARP cache problem?
**To check your TCP/IP configuration open a command window or MSDOS window. Start button, start menu, select the run option and press enter, in the window at the prompt type IPCONFIG /ALL (note: the space between the config and the /all )
**If the arp or dns cache are dirty i.e. have corrupt entries in them you can clean the arp or DNS cache in one of x2 ways. 1) type ipconfig /flushdns or 2) reboot your machine this will have the same effect as 1).
**Ensure you do have the correct F9 DNS primary & DNS secondary server IP address's entered correctly for your connection to the internet. This information will be found under your account details here on the F9 portal.