One page check-out magento is suddenly failing?

I had a working webshop, however, overnight the one page check out suddenly has multiple (probably related) problems.
It started with a failure on the customer’s information, ‘the password needs to match’ – even with guest accounts where there is no password required. It solved this one by:

Find This line in Customer.php $confirmation = $this->getConfirmation();
Replace That that line with $confirmation = $this->getPasswordConfirmation();

This worked, but now I have a failure at the payment method. It seems that it does not run a script. Did I have to change the line of code above in multiple directories? Does anyone else has this problem? I have tried almost everything it feels..

Thank you!