[Logician]

@Kaelon: Try this:
Login PhpMyAdmin and use this command:
REPAIR TABLE post;

Before using it, login Admin CP (if you still can) and disable your board.

You can also try to run repair.php again, but this time after you disabled your board.

Hope it fixes your problem. And if does BACKUP immediately..

@Nakkid: It's not a good idea to repair your database, when someone has access to it. It can cause corruptions. I suggest turning the board off from AdminCP, BEFORE applying any repair (or any direct action) process.

@All: Your database is everything for your board and probably for your site. Dont ever think about to touch it, BEFORE backing it up!

Regards,
Logician