I am constructing a very simple site for a club. The site only has about 10 pages now, a few links to other sites (such a pBase, where we keep pictures) and some links to websites of similar clubs.

Really basic stuff.

A few minutes ago I changed a couple of things on a page - moved a picture to better center it and corrected some spelling errors.

And then I tried to preview the site and received the message that it could not be previewed. This has happened quite a few times in the past day or two. The only way to resolve the situation is to do a restart of the computer. Closing VSD and restarting doesn't help.

John – try this – when you first open VSD, right click the icon and choose "run as administrator". Maybe this will get around whatever is keeping VSD from accessing the internet for the preview.
Let us know how it goes. If that doesn't do it, you could put in a support ticket and get some pro help.