Try going into phpMyAdmin from your Web host control panel
- click on Databases
- click on the database your forum is using
- go to the very bottom of the page and you should see an option to check all tables.
- Click CHECK ALL and that should place a check mark on all the tables.
- Then once again go to the bottom of the page and select in the dropdown box REPAIR TABLE
- It will then work on repairing them if there is an issue.
- Then go back and run the OPTIMIZE TABLE command
Then try to connect to your forums and see if you're still having the same issue.