"Not working" can mean many things. Here are a few common problems:
- MySQL service will not start.
- The service starts, but no programs can connect. Make sure that the user has permissions to connect to the server.
- Queries that worked in earlier versions no longer work. MySQL implemented a few syntax changes with version 5. Of particular note is the change in JOIN syntax.
See also the upgrade guide.
This was first published in September 2006