Excel Docs Open Slowly

If I open an Excel document from the folder it resides in (Desktop, etc.) it can take 5 or more minutes before it opens. If I open the Excel app first, then try to open an Excell doc from it's folder the same thing happens.

However, if I open the Excel app first, then open an Excel doc by selecting open from the Office button (selecting a recently opened one or browsing to the document) it opens normally.

Any ideas?

It makes me think the default program setting for xls files might be broken. So, in a folder, right-click on an excel spreadsheet, in the menu that comes up the 4th or 5th item down should be "Open With" with a little arrow, scroll over that so the sub-menu pops out, then click "choose program" or "choose default program" (wording will vary depending on what version of windows you're in), then make sure the "always use selected program" box is check and select to open w/ excel. Test it a few times and see if that fixes it.