How was the crystal skin installed?
Was the old skin1 renamed or deleted or overwritten?
If you run the install.php file again you will see the option to reinstall the skin, this will reinstall the original. But make sure you backup the crystal skin first.
If you want a very easy way to switch skins in the future, get this, I highly recommend it:
http://www.cart-lab.com/lab/customer/product.php?productid=1&cat=0&page=1