I think you mean the fan belt, too. This wouldnt cause the car to not start, even if you somehow got it ridiculously tight!. If you do mean the timing belt then yes, see response above re getting the teeth lined up. The fan belt does not have teeth, and is the one you can access without removing any covers. As you say it was whistling before you tightened it up, then thats the fan belt, the timing belt wouldnt whistle, or schreech when it slips, in the same way. This type of noise is more common in cold weather, until the engine warms up enough for the loose belt to grip a bit.