First off, your issue could stem from quite different problems and still
appear to be the same issue.
I believe at this point, on the basis of info provided, that your's is
an interference problem rather than a "faulty or defective" circuit.
Both will appear similar in symptom.
You haven't said whether the actual conductors were individually for
continuity, and for correct polarity, but I'm virtually certain that
those are not the issue.
I beleive you're suffering from some signal degradation due to ?
Being how this is a problem, you first off will wish to ensure that you
now install some cabling which is shielded. Category 5 is still what
you want, especially with broadband/optical upon us in many markets, but
you appear to be in a situation in which shielding the conductors (as in
shielded cable) is what you need. This type cabling is available in
types which have a metallic foil surrounding all of the conductors, or
will have a woven wire braid surrounding. In many types of sensitive
applications, shielded cable is required, because a signal is much more
difficult to "snoop" with a wireless "tap" on shielded cable. Well,
you're in a situation where you're more worried about what signals will
be absorbed into the wires, than what is leaking off of it.
Electronic phones, solid state light dimmers, touch-metal light switches
of the type where you touch a metal part on lamp to turn on, another
computer, any other FCC category B devices in home, like digital CD
players, computers, VCRs, digital clocks and thermostats, etc.
Possible things to try before yanking out existing cabling.
Obtain and install "ferite bead" rf filters on each end of each cable
length. These are obtainable where network materials are sold, like
where you buy your rj45 modular plugs and crimper. These will hopefully
attenuate rf interference which the cabling picks up like and antenna,
at either end of the cable.
Try powering the circuit which controls the router/hub/switch on, as
well as just the upstairs computer on, and EVERYTHING else in the house
off. Establish a connection. Then methodically start turning on
breakers in the house till your connection dies. Then, turn on again,
go to that area of abode, and start turning on/off individual devices,
lights, appliances,etc, until you find the main culprit.
Remember that any individual length of cat 5(24 gauge) is only good to
Check out your network card to find out if it has indicators, and how
they work. Many network cards will have one or more indicators, one of
which will indicate if a connection to valid, operating network device
is made, some others will have traffic activity indicators, etc. See
which yours has to see if you are connecting but just not able to
transfer any valid data. A connection indicator would tell you that
your physical connections are good. You could then concentrate on
abatement of the signal degradation.
Another required diagnostic is to take the "upstairs computer" and
connect it someplace else into the network. If it works in another
network outlet, then you know with certitude that it's not a
configuration error, as opposed to a connection or data corruption