Maybe the local copy of your web site has gotten lost or corrupted.  Or maybe you let someone edit your site live on the server from another location.  If so, you need to get a current copy of your site back onto your hard drive.  Here's how.

Create a folder on your hard drive to hold your site

In FrontPage, do Tools > Options > Uncheck "open last web automatically when FP starts."  This will keep you from getting confused in the future about what site you're actually editing.

Then do File > Open Web > http://www.url.com > userID / pw > OK. That will open the live site in FP.

Then with that site open, do File > Publish Web > (in FP 2003, check "File System") > Click the Browse button > Browse to and open the folder you created earlier on your hard drive > OK (in FP 2003, you will click the grey "publish" button on the bottom right of the FP window to initiate publishing.)  FP will ask you if you want it to turn the folder into a FP web. Click Yes. FP will alert you that some of your files may not work properly on your local computer. That's fine. Click OK.