Font Sizes, defaults, change?!

HI, I have a Dimension 4500S and it's been basically problem free, though recently, just today, I ran into some annoying problems. In the past--ever since I got it--internet browsers, word docs, etc displayed smaller fonts (I HAVE NEVER changed the screen resolution), the fonts looked much smaller than those on the same page on my parent's computer. Though today, that completely changed. I have big fonts coming up on the same webpages I download daily...and I don't like it one bit. I can't think of anything I did that could have caused this...except, perhaps downloading a program, then while trying to delete the extra downloads, I accidentally deleted a Windows HOTFIX item from the top of the list.

Anyone know what happened? Or any idea of what I should do?!