davis114 wrote:
If cookies are enabled and you still can't stay logged in, try clearing your browser's cache and history. This will delete any potentially corrupted files. Also, be sure to try accessing your account with several different browsers.
Thank you! Your suggestion to try different browsers led me to try Google Chrome, which worked. I then deleted cache and history on both Windows machines, making sure to uncheck the box that would have preserved Favorites website data, and now login on Internet Explorer works as well on both Windows 7 and 8.
Both Windows versions, including Internet Explorer, were recently updated, so something in that may have caused the problem.
Much appreciation for the help and suggestions of all!