Thank you both for your suggestions. I have been working on both and will try to address question you both have.
First, the other forums have not yet provided any response or suggestions that is why I am so appreciative of your response.
I am running McAfee anti-virus software and I have run a full scan without finding any problems. I keep my definitions up to date and have scheduled scans so I am comfortable there, but, just to be sure, I manually checked for updates and did a full scan without discovering any major issues and had the problem after doing that.
Then I downloaded the memory test software and ran it. There were no errors.
Finally, I booted from my Windows XP CD and chose 'R' for repair. After that it brought me to a DOS prompt and with the message Type 'Exit' to return to Windows or something like that. I have no idea what to do at that point to repair Explorer. Can you provide a suggestion?
Once again, thank you for your help.