Thank you everyone for weighing in to help. I have done a number of things by following various suggestions here and elsewhere, and don't know which one did the trick. Now, I am happy to report that my system finally recognizes every USB device that I plugged in. The last thing I did was to install the SP1 update as was alerted by this thread
http://www.flyertalk.com/forum/showthread.php?t=802723
Thanks again, everyone. ^