Why can i no longer enter text into form fields in Acrobat DC Pro?

I had surgery and had not used my Acrobat DC Pro for about a month. When I tried using it today, I can no longer enter text into form fields. I even uninstalled the program and reinstalled it. Still can't enter text. I'm very frustrated because I love the program and have been using it for a year with no problems. I have Windows 7 Professional on my computer.