Windows 7: text size

I am having problems adjusting text size in certain pop up windows. For example...when I install a game (usually pop cap games) the first and all installation windows have text size so small I can hardly read them. All web pages and folders and everything else I use have proper text sizes for me. How can I change just the text sizes on those install windows? Once upon a time they were of proper size. Just lately they seemed to change on their own. Maybe I clicked on something I didn't realize. Any suggestions? Thank you for your time and help in this matter. I am running Windows 7 Pro 64 bit and Mozilla Firefox.

Finally got this problem solved. I had corrupted Fonts causing the problem. Replaced my Fonts folder and everything is fine.