Recently a couple readers wrote to me with very similar problems. One was having trouble getting Internet Explorer to run; the other, Windows Explorer.
In other words, a couple of Windows' own built-in tools were broken. (Note to Microsoft: That should not happen. Come on!)
Usually, for situations like these, I recommend an end-run around the problem. Internet Explorer won't work? Install Firefox or Chrome and use that instead. Can't load Windows Explorer? Switch to any number of even better Explorer replacements.
Of course, that doesn't really solve the problem. If you're hoping to fix your broken tool, you'll need to do a little troubleshooting. To start, I recommend switching to (or creating) another user account, then seeing if Explorer runs properly.
If it does, you've narrowed down the problem significantly (and should consider "moving" to a new user account permanently). If not, well, back to square one.
Either way, it's a simple method of figuring out how deeply rooted into Windows the problem is. And that will help considerably as you Google-search for an actual fix (assuming there is one--sometimes these things can be resolved only by reinstalling Windows).