Thumbnail suddenly won't show Image of small drawings

I have a library of medical equipment drawings. The files are not very big (one piece of equipment per file) and always have shown an image when viewing the file in the folder via thumbnail view. Now suddenly they do not and I cannot figure out which setting I've screwed up. Anyone come across this?

I've checked all the settings I can think of OS wise (like folder options and such).

I did just recently download InDesign CS5 and I think I remember it asking me something about a thumbnail view, but even then (which ever I told it to do) I would think that would only pertain to that program.....

Try setting your settings back to how they before you installed InDesign CS5, and if that doesn't fix it, then it may lay in the way that you had last viewed the drawing before you save it. AutoCAD trys to save the thumbnail exactly the way you saved it, so it may be either to "big" to view or it may be to "small" to see, but that is rarely a problem... if the problem started right after you installed that program, it will most likley be something that the program touched....

ya, but where do I find those settings? I've checked folder options and such.... don't really know where else to check.