Here is what happened. After the upgrade I contacted IT to see if they had encountered the problem before. They had not. After listening to how they are getting rid of Access (not true), I needed to move on quickly, so I asked him to restore it back to 2013. I later posted the question in a different way and got the response that the Trusted files are kept in a different location. That is why it didn't work.
To answer some of the questions above, everything was in order when the files opened. There was no "enable macros" option, there were no broken or missing references, and all the event procedures were in place. I will be upgrading on another computer in the very near future and will try to Trusted Locations option.
Thank all of you for your help.