I actually just finished up cleaning a virus from my computer (took me in total like 20 minutes, no big deal), but I'm almost sure this is what caused the problem. Now, whenever I download a zipfile I can open it but it will not extract. The Windows Explorer extractor acts like everything went fine, but all it does is create the folder if it doesn't exist and then extract nothing. I also cannot open any file in the zipped folder.
It sounds like the virus may have damaged Windows. Open up an administrator command prompt. if you dont know how, click
Try to re-enable the built-in support for zip archives, as described here: http://codesociety.com/2009/07/27/disable-zip-folders-in-windows-7-vista-xp/
If you're using Windows Xp, you must:
For Windows Vista:
On Windows 7 the procedure is a bit more long, see To Enable Zip Folders on sevenforums.com