99 Sebring Convertible won't start

I have a 1999 Sebring Convertible that randomly won't turn over at all when I try to start it. Here are the symptoms:

1) When it happened last night after work (45 degrees, sunny) the headlights, dashboard and interior lights worked fine but the radio did not.
2) No one can start the car by "jumping it" - AAA guy and dealer failed also.
3) The dealer couldn't figure out the problem either after 3 weeks of trying 8-9 months ago. Once when I went to pick the car up from the dealer, they drove the car around for me, turned the car off, but when I went to drive it home it didn't start - so they pushed it back inside!
4) Not sure if this is a red herring, but I noticed last night that the steering wheel wasn't locked but am not sure if this was normal or not. I tried to get it to lock, to no avail.
5) Don't say the battery - every new person to look at wants to change it - they've done it twice! No more!
6) When I don't have this issue and it's been at least 6-8 months since it happened last, the car runs like new.
7) At one point the dealer was saying that it somehow looked like a seat belt issue, but a few weeks later they didn't seem so sure. I do not have power seat belts.
8) I have a 6 cylinder 2.5L engine
Any Ideas?