My 1st instincts also would have been to delete the LW preferences whilst LW was closed. Since it was working before but only suddenly having problems.

"There is no firewall or router in the Motorola sb5100. It's just a modem and that's it. There is no ports to open up, or to forward." So the problem is probably not with the sb5100 unless it needs repair or something.

Is there any other splitter such as a router?

Another thought is the problem is your isp provider who may be filtering p2p using a special p2p program filter. eg: such a filter But I can't seem to locate anything about your isp.

Did you use these instructions for deleting your LW preferences: Fixes for Limewire (see images below) Rather than delete the LW preferences & then reboot the comp, it would be better the other way around. Reboot & then delete the preferences folder. That's of course hoping you don't have LW set to start at system start up.