If it does absolutely nothing when you turn the key, that is what happens to my car once in a while! The cure (in my case at least) seems to be one of the following:

1)lock and unlock the doors with the key (I have central locking system) a few times.

2) if I parked the car, turned off the engine and then moved the shifter from D to P (without pressing the brake pedal), then all I have to do is push the brake pedal a few times.

It seems to me that it is a computer problem that should not have been there. In my case, it used to happen once a year; lately, it happens a bit more often. By the way, after my car starts, it behaves like nothing happened in between!

Also, twice in the past I called for towing service, and right after that call, my car would start fine and behave fine (hence, I would cancel the call for help)!

I hope this may provide some other experiences.

850T 1995 and 124k miles (the best car I have ever driven so far)
240 1987 (sold it after 250k miles while in great shape)