The non-functioning Show Desktop icon is a separate problem that affects all users. I assume that the Windows Explorer issue from your first post is not present under the new user login.

Your registry cleaner may be responsible for some of the issues. We normally don't recommend using registry cleaners - they can cause more problems than they can fix if you are not careful.

I'd say it is not time to locate your Windows XP CD. If running System File Checker does not correct the issues, it may be time for a repair install.

Before doing that however, it couldn;t hurt to scan for any possible malware.