After changing hosting provider of a phpBB forum you may face few problems.

1. Administrative Control Panel or ACP Panel goes blank.
2. Unread Posts / Your Posts / Active Topics / Unanswered Posts / New Posts etc. are blank.
3. Search function does not work.
4. Database Connectivity issue arise.
5. Missing Post Reply Button.

You need to delete all contents of /cache folder. Make sure this folder is writable.