You haven't said what kind of broadband you have ...
If it's ADSL, I've heard that the ADSL connection can "go stale" and you have to refresh it from time to time by breaking and re-making the phone line connection on the modem or modem/router, or turning it off and back on.
I've had a couple of inexplicable frozen connections and that has worked. Maybe worth a try for you.
More often, I have to re-start the computer (which on my setup does not reset the ADSL connection, just the LAN). I never switch it off - it just goes in and out of Standby and sometimes it seems to get its LAN t*ts in a tangle, but not often. In and out of suspend causes regular problems with the LAN, so much so that I don't use suspend any more. (P4, XP Home.)
Once the problem is solved per the above, it's stable for a week or more. Though that's not perfect, I can live with it.
AA