There is a question that I see several times monthly in TYPO3 mailing lists: "I see an empty (blank) page after XXX. How do I fix it?". Here is the step by step answer:
- Go to the Install tool
- Select "All configuration"
- Set displayErrors to 2
- Add your IP address to devIPmask
Now you will see PHP errors that happen. By default these errors are hidden by TYPO3 for security reasons and it causes blank pages. Changing settings above allows to see these errors on your IP address only.
So fix these PHP errors and your site will be back.