Blank pages usually mean you're getting a PHP error and your server logs rather than displays the error, which is the behavior you want with a production site. You just have to know where to get the information.
You can use your FTP program or the file manager for your server control panel to download and look at the error_log files both in /public_html and in /public_html/wp-admin to see what the actual error is, then read through the Wordpress 3.5 Master Troubleshooting post, following the steps at the end of the first post to identify where the problem is coming from; e.g., from a plugin or theme, etc.
If you can identify what you did--if anything--right before this started happening--like switch themes, install a plugin, or whatever--that may help you identify the source of the problem.