3 Answers

Might have done some serious damage...

http://www.answerbag.com/q_view/533354

You probably burned out a sensor, or on older cars, a voltage regulator.  It is repairable, have you changed them already, and test the battery for power, charge it if needed, then try starting again.  Go to a mechanic friend, local garage, and ask what they think and how much to repair.  When they tell you what it is.  Go on You Tube and find a video on that type of repair, if it looks like you can do it, go buy the part and complete job... Good luck, and learn from this mistake! 

What should you do? Prepare for a very expensive repair bill, and find someone who knows how to correctly connect battery next time! (I think that fairly much sums it up.)