wordpress site very slow

Hello

My site open very slow, http://www.brisvaani.com/
. and sometime shows internal server error.
Site is hosted on godaddy , I have consult to them for any problem in server configuration , they told everything is perfect from their side.

. There are about 2500, post and 1500 users, my db site is approx 180Mb when export in .sql format . Is this is reason for slow site.

If it is, then how to solve. or if another please give some suggestion.
I am in deep trouble.