In comp.dcom.lans.ethernet SparkyGuy wrote in part:
We're having to reset our office network at least once a day. it
locks up and only a power cycle will get things going again.

Have you tried cycling power one box at a time (usually
working from dowstream to upstream) to see if there's
one sensitive box and the network comes back up?

Otherwise, as others have said, UPS. It is far better
than any filter and usually less expensive.

-- Robert