You don't say how many wires are in the box, but it's possible that the wire-nutted connections were not done well initially and simply moving wires out of the way may have loosened one of the connections. Shut off the breaker (or breakers) that control the power to the box, pull the new light switch out of the way, and then check for loose wires by gently pulling on each wire where it is connected with a wire nut to see if anything is loose. It is also possible that you may have a bare ground wire touching one of the live connections on the fan switch. If all this sounds beyond your skill level, please have a knowledgeable friend or electrician check this out.

P.S.: You didn't, by any chance, turn off a switch that is directly mounted on the fan did you?

Thanks, kudzu9. I took the fan apart again and it seems one wire was slightly loose in its connector. I think I let the fan dangle a bit when I was first disassembling it and the weight probably did it in.

Working great now, though. And a switch in another fan just broke, so I guess its back to the hardware store. Do these things have a three-year lifespan or something?? :)

It would be a better idea to wire the fan and light so they operate from a wall switch rather then the pull chain switch that comes with the fan. Another option is to set the fan up with one of those remote packages that will give you the ability to use a remote control to operate the fan or light.
I installed three Hampton Bay fans in 1992 and have never had an issue with the pull chains. Never use them.
Ron