Hot Wheels: Track Attack Q&A

Ok, i have a 6 year old that has unlocked all the cars in this game but one. Of course he wants it but can never seem to get it! I did find a cheat code to unlock all the cars, but i have no idea where i have to go to enter the code! Can anyone help me?

When I put the disk in. The Wii makes a weird noise and after a while it brings up an error saying to press the eject button, take the game out and then switch the Wii off.

What is wrong with it, there no scratches on the disk and the other games work fine.