I have had my site up and running fine for about a year. I just tried to log on to my admin page and it's gone - blank. The files do seem to be there checking FTP. It is run ssl.

I saw an error in the debug log:
PHP Fatal error: Class 'yclass' not found in /home/**mysite**/includes/functions/extra_functions/xsell_advanced.php on line 18

I have not changed any php files in quite a while.

What can I do without the admin page?
Any ideas?

Thanks