Is a ball lifted to the playfield when you strum the coin switch for the first time? If one is, the game behavior you described is normal. Inserting another coin (or strumming the coin switch as you are doing) should result in the backglass flashing and the occasional advance of odds and other features. Basically, the game is allowing you to insert more coins in return for a bigger payoff if you have a winning game. If a ball is in the ball lane, shoot it. If no ball was ever lifted to the playfield, you do have a real problem that folks here will help you with.