You do know you can run the 'check_requirements.php' in the Tools directory of your IP.Board 3.0.x file download.
Just upload it to the server and check if your host/server is missing some of the requirements. (Upgrade shouldn't have worked if you are)...
As for the other errors, goto Support and run the Diagnostics Checker on your database, and make sure nothing in your database is corrupted. After that, run the Permissions Checker to make sure every file/folder specified is readable and writable. Uhm... In System, click Cache Management, then "Recache All".
If you are still having skin issues, recache the skin in your Look & Feel, then if your STILL having issues, find a way to reinstall the default skin, or even revert all customizations (goes to default ips pro).