Here at last is something that's never happened in my experience. Let me know if it's befallen you.
I am, as is my custom, wading through my various e-mail accounts, when a message from my wife pops up in my Yahoo account. I click on it, of course, and the message displayed is an ad from HP Home & Home Office Store. I assume that I clicked on the wrong line in the message queue, but note that there is no "previous" link even though my wife's note, being the most recent, was at the top of the list. Back to the message queue, where I observe that the HP message is actually three messages down the list from my wife's, making it pretty unlikely that I clicked on the wrong line. Try, try again...and here's the HP message again!
Back to messages, where I click on the HP message, and am rewarded with the latest Nikonians Newsletters, a message that appears four places down the list from the HP message.
So I close the tab in which I had Yahoo Mail running, create a new tab, re-enter Yahoo Mail...and presto! everything is working again.
Just when a guy thought he had seen it all...