Hi,
PayPal Express checkout indeed permits payments with credit cards without creating an account, but that's not the only one. The normal PayPal Standard also permits that.
That is however only possible if the PayPal account is a Business account and only if the corresponding option in your PayPal account is activated:
www.paypal.com/cgi-bin/webscr?cmd=p/mer/WAX_landing-outside
So first, check that option.
On top of that, PayPal might still not allow users to purchase without a PayPal account as it tracks them and their purchases with several means: cookies in the browser, their email address, their country in their address, their IP address.
So it could be that PayPal has flagged you to not be able to pay without an account.
The best you can do is to contact PayPal's support so that they can check on their end why you wouldn't see the possibility to pay as a guest on their payment page for your website.