Database Error with correct DB info?

So, I’m building a site for a client, and we’re migrating from my dev server to their live environment and have hit a hiccup: The dreaded “Error establishing a database connection”

I’ve done a check of the connection info (Hots, username, password and db name – and that worked no problem. Trying to get to domain.com/wp-admin suggests a DB repair, but when I click the button, all I get is an “Are you sure” with no way to confirm.

Anyone got any ideas?