Its difficult to see any problem without access to site or server.
If its possible, can you give me ftp access and send me the details via pm so I can take a look for you?
There's been some issues around the new database layer with certain hosts, it relates to PDO availability somehow. Before you try anything, try removing the local php.ini files as I've heard a few reports of these somehow unconfiguring PDO.
If that doesn't help, try reverting to the old DB class by deleting includes/class.database.php and renaming class.database_ORG.php to class.database.php
this step
"If that doesn't help, try reverting to the old DB class by deleting includes/class.database.php and renaming class.database_ORG.php to class.database.php"
helped me and now there is no Error HTTP 500, but i have an design error you can see www.sefone.com/gggg how i can fix this?