97 Taurus will not start

I need some help? I left the key turned in the on postion after rolling up the electric windows and the next morning the car would not start. Of course the battery was dead. So I charged the battery and it still would not even turn over. Next I took the battery out and had it tested, all O.K. The guys at auto parts store said to test the starter, so off came the starter and all was ok with it? I did find that when I reconnected the battery cable the horn started going off and the interior light started blinking, I did not know it had an alarm? It is not after market and the owners manuel said that if you insert the key, unlock the doors it would go off? If I pull the fuse for the horn and then connect the battery and replace the fuse it does not go off? Anyway the car wont start and I hope somebody has an idea?

Update! I do have lights, horn, radio ect.. All fuses seem to be ok.

Does anyone have any suggestions?

I went to start my 97 Taurur LX DOHC and it would turn but not fire, I found out that it was a bad pats key. does your car have the bigger key? it may if it has the alarm system! the Pats key is deffinitly larger than that of a normal key! and the key fobs are really easy to program if you get one off of ebay or something! I hope this helps you!