Content types do not get listed When I am logged-in as administrator, I click on content, then add content, and I get a message saying I have no content types created, and I must create new ones. In fact, though, I have several content types, and I have been using them for days to build my site. 

Do you have any idea on where the glitch is?
It would appear that this is a very good candidate for your issue:

http://drupal.org/node/997444

Assuming you have altered your navigation menu, which many people will do when they are new, you may have inadvertently removed your access. Re-enable this access and you should be good to go. If this does not solve the problem I do not know what it would be.