having database error

[p@ndu]

i am getting this database error can some one tell me the solution

Database error in vBulletin 4.0.2:

Invalid SQL:
SELECT COUNT(postid) AS posts, COUNT(threadid) AS threads FROM post;

MySQL Error   : Table './******_downloadsmasti/post' is marked as crashed and should be repaired
Error Number  : 145
Request Date  : Monday, August 16th 2010 @ 11:13:02 PM
Error Date    : Monday, August 16th 2010 @ 11:13:02 PM

IP Address    : 202.65.***.***
Username      : *******
Classname     : vB_Database
MySQL Version : 5.1.48