Restore the backups that you made before the upgrade - you did take backups didn't you?
The main issue here is not reading the available information before going ahead with a major upgrade.
Upgrading from 3.0 to 3.2 wrote:phpBB 3.2 is not compatible with 3.0 and most of the previous files will need to be removed prior to upgrading.
Upgrading from 3.1 to 3.2 wrote:phpBB 3.2 is not completely backwards compatible with 3.1 and custom edits may no longer work. The easiest upgrade method is to remove all existing files prior to upgrading and re-applying custom changes after verifying their correctness.