What's wrong with my custom patch cables?

Double-check that the ends are on all the way. When you look through the end of the connector, you should be able to see the shiny copper tips of all the wires flush with the end of the connector.

If that's not the problem, it might be that you're getting crosstalk if you didn't follow the proper pinout.

Be sure to wire them correctly, according to the TIA-586B standard. There's a howto at http://www.edpscomputing.com/network.htm which you can use (scroll to the bottom).

The other answers hinted at this, but I'm going to underscore it:

Pins 4 & 5 (the centermost two pins) must be on the same twisted pair.

Pins 3 & 6 (the pins just outside of 4 & 5) must be on the same twisted pair.

If you wired it "straight-through" as you said, without knowing about the special pairing requirements, then you probably did your pairs like this: (1 & 2), (3 & 4), (5 & 6), (7 & 8). That just won't work. You would've got pins 1, 2, 7, and 8 right, but pins 3, 4, 5, and 6 would be wrong. (I'll spare you the details of balanced-line transmission and noise cancellation.)

So follow the TIA/EIA-568-B standard as rob mentioned. Not only will it get the pairings right, but it'll make it easier when you or someone else has to work on those cables again.

One other thought: Inside the RJ-45 plugs, you know the little teeth that pierce through the insulation of the individual wires? The design of those teeth can be optimized for solid conductor wire, or optimized for stranded wire, or designed to work okay with either. If you happened to get the kind of RJ-45 plugs with teeth optimized for the opposite kind of wire from what you're using them on, they may not work reliably.

It going to be hard to tell you what exactly you did wrong. My advice would be to cut the plugs off and start over following a guide like this one from Lanshack.

Ok maybe I'm overthinking it, but as another poster said this is going to be hard for us to debug. You could get a multimeter and do a continuity check to figure out which pin on one end is wired to which pin on the other end. Then check to make sure it's TIA-586A|B. It'll also tell you whether you're making contact at all.

If the cable is as you expect electrically, then I would start looking at things like interference or cable length. Are they too short? Too long? Bad shielding? I can't imagine simple interference is preventing a link light, so it's probably not electrically connected.

I've just learned how to make these cables at work, and I've had good luck so far, so let me tell you the procedure I use:

1. Carefully strip about an inch and a half of outer plastic from the cable
2. straighten out each of the individual wires and get them in the proper order. Spiff listed the order correctly, or you can google the specification to get the "official" color ordering. (note: the actual color doesn't matter, just that the colors are paired and both cable ends are identical)
3. NOW is the time to trim the wires to length; You should trim them to about a centimeter, or you can look at an RJ45 head for guidance. The wires should be long enough to reach the end of the canal so the gold heads can be pushed into them when crimped, and the outer sheath should be in position to be grabbed by the square hole thingy on top of the head.
4. Stick your head on and double check to make sure that the wires reach all the way down the canal so it gets properly crimped.
5. CRIMP! Squeeze it down all the way and make sure you seal it tight. Then visually inspect everything for a tight seal, and test once you have your testing unit. Hopefully it should work.

Crimpin' people, now that's what it's all about, yo.