Network switch lockup

Hello,
We have a "cheap" unmanaged Linksys switch for our 20 PC network.
On occasion, it "locks up". Systems are all up, but no PC can ping
another. We had the same problem with another switch that we replaced
with the Linksys. I don't think it is an environmental problem
(electrical, etc).

If I buy a managed switch, is there somehow I could see the traffic
running
through the switch, to see if it is just getting overwhelmed with
traffic?

What combination of hardware/software could I use to diagnose this
problem.
Hopefully with free/shareware.

Thanks!
Japhy