Things that spring to mind are:
- Rename your Calibre Library folder so that Calibre cannot pick up a (possibly corrupt) metadata.db file.
- Remove your Calibre settings (uninstall does not). They should be under your User Profile. On my Windows 7 system this is in a Calibre folder located at C:\Users\username\appdata\roaming, but it can be different for other versions of Windows (e.g. under Documents and Settings). Delete (or rename) the whole calibre folder.
- Check the search path in case there is some other Python related folders ahead of the C:\Program files\Calibre2 that is the normal Calibre one.