First let's see if we can make that white page display an error. As normally a white page is basically suppressed (silent) error. This assuming you were not playing with templates as I have seen someone mess up their css so bad that it failed to load, but we'll assume add-on conflict or host issue.
Add this into your config.php
$config['debug'] = 1;
This will place your site in debug mode and should in theory display an error. Post it here. If you don't get anything, don't worry to much about. But it normally will spit something out.
Next, you should remove that and add this
$config['enableListeners'] = false;
This generally will turn off every add-on. If your site loads after this, then you know for sure its an add-on issue. Then its only a matter of a process of elimination.
If you're site still is all white, my question will be what have your changed (if not you, your host)?