Issues Checking Out

Earlier when I was trying to check out, I tried to update my payment details via the check-out cart. When I clicked 'Submit', I got a 404. I then went into my account details and manually updated the info there. However, when I tried to check out again, it kept asking me to "Please select a payment method". I did this multiple times, but nothing happened. I've tried everything, but I just cannot check out no matter what I do. Looks like I might be taking my business to Amazon......