Boxster not starting properly

[charlesd]

Many days the car starts normally. Other days I can turn the key, lights come on, but there is no clicking and the engine doesn't even try to turn over. I will turn the key and hold it for more than 5 seconds and nothing. Sometimes the second time I turn the key it will start and sometimes it takes as many as five times. Sometimes when I turn the key it feels like it turns too far.

The dealer has checked the battery, alternator, clutch switch and says they can't find a problem. They kept it for a week and said it started no problem for them every day.

The problem happens most frequently after it has been sitting overnight or when the engine is cold. It is usually starts on the first try if it has been running and the engine is warm.

Does this sound like the ignition switch? The starter? I've also read the cables that run to the starter/alternator can cause this, but it seems like that is usually when the car is warm.

I have a '99 Boxster 5 spd with 135k miles.