02 monte carlo, we pulled the car in the shop to clean the battery terminal....when we reconnected it the car wouldnt start, the radio said it was locked, and my check engine light is on along with the security light, service vehicle soon, and change engine oil light...checked battery and it is fine, so we took the positive cable back off and reconnected it again and then the horn started to chirp every 3 seconds, and also we have no head lights...any help would be greatyl appreciated
thanks