[TYPO3] FE empty after moving Typo3 and update to typo3 4

[Andreas Balzer]

Hi! I downloaded TYPO3 3.8.0 from my server, changed all paths from 
"/contents" to "/" and integrated Typo3 4.0. Then i uploaded everything, 
  went to the install tool and selected DB Analyzer > Compare and 
selected everything. (Add some tables, delete some unused stuff 
(extensions that were deinstalled)

Then i hit update and finaly checked and updated the DB references in 
the BE. Ok.. The BE works fine, everything is there. But the FE is 
completly empty. Nothing visible.. not even a single char in the 
sourcecode of the FE..

What do i have to do?
Any help appreciated.

Greetings
Andreas