by yvan vander sanden.
Ok, all is working now. It turned out to be a combination of 2 things.
Key to solving it was to turn on display of warnings and errors. After that, I discovered there was something in my config.php related to an old module that i didn't install anymore. (removed it during upgrade)
Second, it appeared that the theme i used (generated with artisteer) was the problem. Switching to another theme (but only after fixing the config problem) solved the problem.
I hope you get yours fixed also.