99 deville wont start

I have a 99 deville the battery was removed and new put in a month later.
Now the dash says anti theft problem car may no start and it wont!!!
The car turns over strong but is not even trying to fire.
Is their something i can do reset or something? The dealers rape your $$$ everytime you walk through the door.:banghead::banghead::banghead::banghead::bang head::banghead:

Check the computer codes to see what is wrong with the theft system.