500 Error (or Unable To Connect To Database?) On Front End, Not Back End

Hello!

I was trying to get my Photo Cart site working again, but that doesn't look like it will be possible. Not the end of the world. However, in doing so, I'd contacted my hosting company to resolve the issue, and now I have an issue with my Sytist site (Photo Cart was in a subfolder, so there shouldn't have been any change to the main directory). It *had* been a 500 error a few minutes ago, but now, after contacting support again, it's "Unable to connect to the databaseAccess denied for user ''@'localhost' (using password: NO)". I don't know what they're doing, but I'm definitely getting the runaround. The latest assessment is that the setup.php file is missing. Is that possible? And, why does the admin work, but not the front end? And, why can I access the front end on my phone, but not on my laptop? Support couldn't answer those questions. Do I just need to get a copy of the setup.php file and stick it up there? I don't have one of those in a subdomain, so that doesn't seem right to me. What am I missing?

Thank you!!

You can email me your website address and hosting account login to look into it.