You say this happens when you go online. I'm inferring, then, that you mean it happens ONLY when you go online. It could be a problem with the modem, or it could be a conflict between the mouse's software and some other software. One thing you might do is see if you can isolate a program that may be conflicting.
You can do that be going to Start > Run and enter MSCONFIG. Then go to the Startup tab. Record everything that is checked there now so you can restore them all later--or at least the ones you want. Then remove all checks except for the System Tray (SysTray.exe). (You may already know a lot of this stuff, but, in service to you, I'm detailing it, anyway.)
Reboot and see if you still have the problem. If you don't, it is one of those programs. You can then restore the programs one by one, rebooting each time, until the problem reappears. If this does turn out to be the source of the trouble, you will know what program is causing the conflict, and you can uninstall it. If it is one you want to keep, you perform a clean reinstall of it, and of the mouse's software, by the way.
I don't know if this will help, but it is a possibility.