Are you attempting to import a backup through PHPMyAdmin? You'll likely hit the PHP max execute time if using a large database.

I would recommend importing a database via command line vs through a web script; I have some instructions in the "Import Database section of the "Migration Guide" at UBBWiki:
Now that the old files are on the new server, you need to import your database; you can again use PHPMyAdmin or use the command line to import the database. The command line way of doing this (note, this is not the MySQL command line, simply the Linux command line) would be:
mysql -h localhost -uuser -ppass database_name < databasebackupfile.sql

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