What causes network cable to not work?

You don't say how you've bundled them together. Did you use zip ties and pull them tight? Did you loop the cable and cinch the loop (like a figure eight)? Are there any other places where there are sharp bends? How small is the radius of the loops or bends?

You don't say whether they're pulled through walls or drop ceilings. You don't say what the conditions are that you're working in. Stray nail tips and sheet metal edges, etc. Are you running parallel to any fluorescent lights?

Besides squirrels and rats (which can be very real problems), most of the time it's rough handling or improper termination that cause problems.

You say "I punched a few jacks on the end of a length of cable". I presume that's just an imprecise way of saying "I punched one jack at each end of a length of cable" because you can't punch a few jacks on a cable for networking and get away with it like you might for multiple phone jacks on one cable.

Also, continuity and "polarity" mean essentially nothing. Your test with two computers or a computer and a switch or best-bet rent a proper Cat 5 or greater tester will be the only ways to approach testing. Lots of things conduct current that won't work for networks.

Also, don't trust patch cables. Try another one.

In addition to having correct cabling (which you can verify by checking that the link light is showing active on both laptops), you must configure the TCP/IP stack to communicate on the same subnet with the same subnet mask and Unique IP's for both computers. Since there is no switch present, you must configure TCP/IP manually with STATIC IP addresses. Can you confirm that you have completed this step? Note use 192.168.1.0/24 (255.255.255.0 mask) if you want to conform to private network standards.

Update: If you've already confirmed the X-over cable alone allows pings, then confirm adding a non- x-over (regular) patch cable and simple cat5 cable connector (back to back rj45 plugs) into the line also passes the ping test. If not, get one of each that you can confirm work.

If those work, and you now try patching over the cable run. If it fails at this point you have positively confirmed you have a bad cabling install. This can be the result of either bad punchdowns, or a break inside the wire run itself. You can use a continuity tester to check each pair of wires by doing the follwoing:

Bare the ends of all the wires on one end, then twisting each colored pair together making sure to keep them isolated from the other pairs. Go to the remote end and apply the two sides of your tester to each of the wires in the pair. if the light lights the wire run is intact (not necessarily good, but intact). Test each pair this way.

If all your pairs test good, punch down your ends again. Now purchase a cheap $10 wiring tester. Hook the two ends up and watch the tester confirm your wiring is correct. If you get green lights on all 4 lights, your punch downs are good.

Now hook your 2 comps up again using the known good cables. If you ping test still doesn't pass, I would guess that you have some major interference in your cable run. At that point I would consider calling up a professional cable installation company for advice, as they will need to inspect your cable run.