I have a 2000 Disco, I went out to start it today and the key does not turn. I have never had this problem before. The battery is fine, any suggestions.
I'm thinking its an alarm thing.

 

That happened to mine last year and I had to order a new switch. They're pretty pricey if you order a new one coded to match your remote/key combo, so I hope you can wiggle it enough to make it turn. Keep in mind that if you just order a different switch then it won't work with your remote key, so you'll have to still carry the old key to unlock the doors. To avoid that, I sent in the old switch and had Land Rover send me a new switch programmed to work with my old key so everything still works with it. It took a few weeks so my mechanic put in a used switch he had to get me going until the new switch came in. I hope you don't have to go through all that though,because it's an expensive PITA.

 

This sounds stupid but it happened to me before with a Ford, turn the key over. With double sided keys one side will wear more than the other because you use it more not even realizing it and then it will not work. Turn the key over and it works.
In my case I had a second key made and one of the sides wasnt right and it didnt work.
Good luck.

 

It is not the alarm.
So if I read this right, you can get in thru the drivers door lock just not turn the key???
Is the steering wheel locked, have you tried turning the wheel hard left or right while turning the key??