404 Error in theme, dashboard

My client has been having major problems with her site using the Lifestyle theme.
She doesn't think she had done anything other than attempt to add a new post.

It was after this that she contacted me.

Her site displays a 404 error in the upper right corner. The Header is missing, as well as all the featured posts.
The menu and sidebar remains. Clicking on any menu item takes you to the page, which looks fine except for the header remains missing.

The real problem is that I am unable to login to the back end. It simply says "404" on the page and nothing else, including NO dashboard.

The hosting company keeps insisting it's a code error. But since I cannot login, I have been unable to verify that,

After escalating the issue with the host, and asking them to try to restore the site, this is the best they can come up with:

I attempted to call your IT person, Steve, as your ticket was escalated to me and had no answer. However, I do have an answer in regards of your WordPress admin login giving a 404 error. It has been concluded that your issue is related to your wp-content/themes/lifestyle directory.

During the investigation, I checked the database tables and everything was fine. I then, for testing purporces renamed your the lifestyle directory to lifestyle.off and managed to get into your wp-admin section and log into it. Please note, I have renamed again to lifestyle. I have also reviewed the backups that we had available and unfortunetaly, the content we have is the same as the live content.

Please have your IT person to check the wp-content/themes/lifestyle or possible re-install your theme. Unfortunately, this seems like a premium theme that you have purchased as their site is listing a price for it, therefore, we do not have the ability to re-install this for you. I have now closed the ticket, however, if something else shows up, a new ticket can be created.

Since I have the theme files, I used Filezilla to re-upload my copy of lifestyle to the "Lifestyle" directory in wp-content > themes

At first I saw the error message below...and still have a 404 and no dashboard.
Please help. I'm not a code expert, and my client is at wits end.

http://blog.brooksgoldmannpublishing.com/

Error establishing a database connection

This either means that the username and password information in your wp-config.php file is incorrect or we can't contact the database server at sql5c40a.carrierzone.com. This could mean your host's database server is down.

Are you sure you have the correct username and password?
Are you sure that you have typed the correct hostname?
Are you sure that the database server is running?

If you're unsure what these terms mean you should probably contact your host. If you still need help you can always visit the WordPress Support Forums.