I don't know how you manage, but I'm getting more confused with each response you give.
dcporter:
I placed my Zen Cart files into a sub folder of my main site. Examples of the two sub folders to my Zen Cart are:
/public_html/(my main site folder)/(Zen Cart folder)/includes
/public_html/(my main site folder)/(Zen Cart folder)/store
Firstly, 'public_html' is the 'main site folder' for almost every server on the internet, ergo, I can only guess what you are considering to be the 'main site folder'.
Secondly, regardless of what or where the 'main site folder' is, a typical ZenCart installation will NOT have an /includes folder and a /store folder inside of it. If it does, I've no idea how you got it there.
This may make a bit more sense if you use actual file/folder names rather than (my main site folder)/(Zen Cart folder)/
Also be aware a location that contains 'public_html' is NOT a URL (website address). It is a FILE LOCATION. Do NOT confuse the two.
dcporter:
I set the site up a couple of weeks ago, then had to leave it, without finishing.
Hmm, brand new site. Never worked properly since installing. Confusing and/or non existent folders being referenced. Internal links going to invalid pages.
In my opinion, scrap this installation and start again... it's probably going to be a heck of a lot quicker than the approach currently taken.
dcporter:
When I came back to finish it I could not access the temporary (or demo) cart site.
Again, more confusion. What is this temporary/demo site that hasn't been mentioned until now? How does this relate the current site (which I assume is not the demo site)?
dcporter:
I tried to access it through admin by clicking on "Online Catalog" but the page that came up said there was a database error.
I have asked you about this on two occasions now. I even rephrased it the second time around to help clarify things. I am still awaiting a response.
dcporter:
What I thought was a direct link to my Cart site did not work.
Yes, we have already established that this is one of your issues, which then led to: My question is, in what way does the URL differ when you hover over the link?
dcporter:
So I'm simply trying to figure out how to access my site.
I'm simply trying to get some definitive responses so that I can build up a mental picture of what is going on that could possible cause your problem(s).
I'm not really getting the responses I need, and those I am getting seem to muddy the waters even further.
dcporter:
Hope that clears it some.
I wish it did, but we have now gone from trying to solve one mystery "When I click Online Catalog in my admin panel the store doesn't load. What comes up is an error page that says Problem connecting to our database" (Which in itself should be quite easy to debug) to the situation whereby I'm no longer sure that anything about your installation is actually 'correct' for a typical 1st time zencart installation.
eg:
/public_html/(my main site folder)/(Zen Cart folder)/store - Not normal/typical (although not necessarily wrong).
http://www.(mysite.com/(renamed cart folder)/ - Not normal/typical. The admin folder is to be renamed, not the cart folder.
If either of these were wrong I'd expect a lot more serious issues than the one you are describing. Why isn't that the case?
I really don't know where to go from here, other than as suggested, a fresh install....
Cheers
rod