Wordpress blog is now showing Install page ? the db is still there and wp-config has correct details

I am not sure what happened but I just looked at my wordpress site and it is showing the install page /wp-admin/install.php instead of showing the blog content.

1. I checked wp-config and it has correct database details
2. The database also exist and has all the content

What is going wrong and how can I fix this ?

Typically, this occurs when one or more of the database tables are corrupt — wp_options in particular.

Try issuing check table and repair table statements accordingly.