Error establishing a database connection

I have 3 active blogs on addon domains. The parent domain is http://www.mistywindow.com/. Two blogs are OK, but my main one at the add-on domain http://mywitsend.co.nz gives the above error when opening in a browser:

1. I had not made any changes since the last successful logon in a browser.

2. A database repair but it didn’t fix the problem.

3. Bluehost said this:
“We apologize for the trouble you’ve been having, there was a bump in the msql service all should be working now however”

4. It hadn’t fixed the problem. Eventually they suggested that I:
“logon and change the theme to default then back and everything should work.”

5. If I login here:
http://mywitsend.co.nz/wp-login.php?redirect_to=%2Fwp-admin%2F
Logging on appears to work, but I can’t actually go anywhere from the logon.

:o(

I’ve tried going directly to various PHP pages after logging on. Just a blank page.

Do I need to bite the bullet and get on with my life?

Help!