I've got a similar problem (well, similar after you've replaced the electrical part of the ignition switch).
It happened intermittently - turning the key to the on position, all the dash lights light up, stereo on. But when turning on to the next position to start the car, nothing at all...
Tried it many times and finally after about 20 mins it started and was fine after that, until afew days later... same thing happened..
In my case, pulling up the codes it showed "an unknown key error". I believe the led on the dash also flashed differently (multiple quick flashes before going to regular slow routine) when you locked the car - yes, the lock and unlock still worked.
My mechanic took apart the key fob and the tiny capsule (transponder) was dirty, cleaned it up and the car started but it didn't last long, the same thing happened after a while... Ended up buying a new key fob and reprogrammed the codes... has worked fine ever since.
Check the error codes to see if you've got the same problem...
You can also try using your spare key to see if it starts.... in my case every time the car can't start, my spare key was 300+kms away.
