OK thanks for coming back to me Buck. In fact, I had already tried what you suggested, and was unsuccessful. But I finally thought to ask my son. Stumped him for quite some time, but eventually he decided the problem was McAfee, which I had "sort of" suspected, and after working on it for a while, he finally figured it out. To solve the problem, click on "Start", and then click on McAfee Privacy Service. Then click on "Administrator" (or whatever user you are), then click on "Edit", then click on "Cookies", then click on "Prompt", then click on "OK", then click on "Edit" (yes, there are two "Edits" in this process!), then click in the radio button for "Web sites that cannot set cookies", then select the site for which the cookie is being rejected (in this case, Yahoo.com), then click "Remove". Now you can cancel back out of the menus: that process solved my problem.
For some reason, McAfee, when it sees you reject a site once when you are in the "Prompt" mode, assumes you want to reject it forever, and to correct the problem, you have to go through the above process.
Well, again I thank you for coming back to me Buck. Sorry to have taken up your time needlessly. Next time I'll know to ask my kid first and maybe save us all a lot of time!
Take care and have a great New Year!
Robert