My experience with Excel is woefully out of date, but as I recall from my days in Microsoft Tech Support my first thought would be there has been a change in the typeface or point size that is creating the problem. Even the same typeface and size from a different font factory could do it. Has anything that might effect the font changed on your system changed since the last time you opened that file? On the assumption Excel is using the default application font, you could try reducing the Application font size. My go to app for that is Marcel Bresink's freeware app
Tinkertool but there are a number of others both free and not free.
