Make sure that the page is still there. You never know when someone else may remove a page you've linked to.
Make sure the file is still there.
Do not change the case on the filename or the path. Typo3 does not change the case for paths to files as it does with pages.
myfolder/Docs/ThisIsIt.pdf
to Typo3 is a totally different file than:
myfolder/docs/thisisit.pdf.
So make sure that you have not accidentally changed the case.
A common issue with images is the changing of the case of the file extension.
myImage.JPG is a different file to Typo3 than myImage.jpg.
Finally since a page linked to a file has to be an external URL, make sure that the url to the file starts http://www.creighton.edu NOT http://typo3.creighton.edu. If a user is in our network (as you usually are if you are on campus or using a VPN to work on your site) the typo3 address will work. Once you are outside our network, it won't.
Recently I was alerted about a link that didn't work. But it should as the page was obviously there.
I looked at the page tree, the page was indeed there, so was anther page with the same exact name (although it was hidden). I think the user had hid one, then created a new with the same name.
You cannot name a page with the same name, even if you hide one.
For more on what happens when you do this please go to modules/info/speakingURLmanagement.