After uploading the files and trying to startup the upgrade process something weard happens, the site cannot be reached anymore. Logging in to the admin is still possible however there is nothing to see there anymore

When trying to reach the url mysite.com/install/upgrade.php a weard page with incompete content shows up, looking trough the source didn't clear things up also...

Dowgrading to a previous version didn't solve the problem to...
Is there something in 1.7 different this time whart causes this? I'm running cmsms for a long time never had any issues with upgrading....
Going to sleep over it now and run a backup on a previous version again tomorrow with a new clean database...
Happy easter!