Font issue in Windows

Recently I had a problem with fonts in Windows (mostly Firefox) suddenly showing up as serif instead of sans-serif. Anyone who uses computers often enough will notice the difference when sans-serif fonts are substituted with serif fonts or vice-versa. Another side effect was that the dots that normally show up for the password textbox on the Windows login screen showed as boxes one day, which usually means the character can't be rendered. The next day the dots came back, but they looked as if they were set for subscript (lowered), and it looked all wrong.

I found a solution by following this link on About.com, found through my friend, Google. About halfway down page two, there is a section called Could your fonts be corrupted? This got me to thinking...