Connected the battery in car backwards now car won't start?

Ouch...

Unfortunately there are quite a few components that are transistorized, and any one of them could have blown transistors when the battery was connected backward. You can pretty much count on the alternator being fried since there is a diode plate that will not have tolerated reverse polarity, as to the computer and ignition system, it's anybody's guess. It all depends on whether the manufacturer anticipated that kind of mistake.

Check the fuseable link.