I installed boot camp on my MacBook and attempted to install Windows XP. When prompted to enter the Product Key, I did but received a message that the product id was invalid. I purchased XP Pro and it has Proof of License COA. Anyway, how do I exit? If I restart the computer and hold the Option key, I see a large padlock icon with what looks like a text box (but I can't enter text) and a clickable arrow that does nothing when I click on it. How can I get back to OS X? Do I need to reinstall OS X? Help!