Is it one where everything looks ok, then just "dissolves" into giberish? I had that problem a few years ago. I cured it with a little gem from Microsoft called "Tweak UI"
Go find it and grab it. It adds an icon to your control panel with lots of nice little things it will let you do. One of the added features is "Rebuild Fonts".
Oh and, as for my glitch, it affects only portions of the fonts on certain web pages and even when using Windows Explorer. For instance, when I open My Documents, the "My Documents" which is displayed with sky background appears to be an extreme "data" type font. This same font appears only on portions of some web pages - my Ameritrade account for instance.