Thanks for your time and suggestions. I will try the suggestions I can (unfortunately, I don't have access to a Windows 7 installation disk), and let you know what happens.
Right now, I'm leaning to a hard drive problem of some sort, as my anti-virus software is active and up-to-date. (A virus isn't impossible, of course, but given no one else appears to be experiencing this issue, it would need to be pretty selective. But maybe I'm just lucky.) In addition, when running certain programs, I was getting some laboring sounds from somewhere in the computer which I interpreted as a fan working overtime in order to cool things. In retrospect, that might have been a naive assumption on my part.
If I can bother you a little bit further, can you clear something up for me? I was under the impression that the recovery disk would let me boot from the disk, without requiring access to the hard drive. Is this another example of naivete on my part?
Again, thanks for your help.