Database Error

[ErrorLog]

Database error in vBulletin 3.8.3:

Invalid SQL:

SELECT MIN(postid) AS postid
FROM post
WHERE threadid = 16920
AND visible = 1
AND dateline > 1246749815

LIMIT 1;

MySQL Error : Table './xxxx/post' is marked as crashed and should be repaired
Error Number : 145
Request Date : Saturday, July 4th 2009 @ 04:49:35 PM
Error Date : Saturday, July 4th 2009 @ 04:49:36 PM
Script : http://xxxx..com/showthread.php?goto=newpost&t=16920
Referrer : http://xxxx.com
IP Address : 88.228.90.173
Username : ErrorLog
Classname : vB_Database
MySQL Version : 5.0.22


Please help me.