I installed 'change db prefix' wordpress plugin (WordPress version being used is 3.7.1), which resulted in an error and has blocked all kind of http access to the site (domain as well as /wp-admin pages). 

Got the following errors while installation -
Changing value: mdv\_user\_roles in table mdv\_options: Failed
Changing values in table mdv\_usermeta: Failed

This is what is happening now -
Whether I try to log into my /wp-admin or just access domain directly I am redirected to /wp-admin/install.php (welcome screen to install WordPress) as if this is a new installation.

Findings -
I logged into phpMyAdmin from cPanel and found that all tables have old prefix, which means none of the tables are changed to the new one. Makes sense, probably there was a db-rollback due to the db errors.

However, $table\_prefix property in wp-config.php file was changed to new prefix. I changed it back to the old prefix and uploaded file to server.

I still get the same behavior though. Access to domain points back to /wp-admin/install.php file.

Anyone has come across this issue? Any help is greatly appreciated! Thanks.