Here's something you can try to test your bookmark,

Tap the Alt key on your keyboard to open the File dropdown menu,
Arrow over to the Favorites tab, then arrow down to Organize favorites.

There are a couple of buttons in there, but keep tabbing until you get
to the list view of your bookmarks.

Arrow down until you find a bookmark that you want to work with, then
press the application key or the Shift key plus the F10 key to open
the context menu and arrow to the selection titled properties and
press the enter key to open it.

Tab around until you get to the URL location textbox, then press the
Ctrl key plus the letter A key to highlight the URL, Press the Ctrl
key plus the letter C key to copy the URL to the clipboard.

Now tap the ESC key to close the properties window and tap the ESC key
once more to close the Favorites window.

Back at your browser, you can press the Alt key and tap the D key to
jump up to the URL location textbox then Press the Ctrl key and tap
the letter V key to paste in the URL from your clipboard.

Press the Enter key and see what happens. If you go to the desired
webpage then the URL was good, so maybe your bookmark has become
corrupted.
so while your at the correct page make another bookmark.

Then test your new bookmark and see if it works.

If the page was indeed gone or incorrect, you could find it and create
a new Favorite book mark or copy the URL and go back to your favorites
and update the URL for that bookmark manually.

If neither of these options work, post back here and let us know.

HTH,
Blaster