Dreamweaver 4, mac os 9

I have been maintaining a website for 6 years.
All of a sudden I have been having problems with previewing my pages in the browser. I can open a dreamweaver document and the pages preview just fine. But when I close down the page and just click on the file to highlight and then select preview the navbar and the headers all come up as missing. I have always done it this way to be able to check just one file. Why all of a sudden does it not want to work this way.

Any help would be very much appreciated.
Thanks