Seems to be a common problem from what I have googled. However, unlike most everyone who has posted on the subject, their failure at login was due to a Wordpress upgrade or a new plugin or a change in hosting companies.
For me, nothing has changed. Hell, I don't even know what version of Wordpress I am running because quite literally, I haven't changed a single thing about my Wordpress setup for at least 6 months... probably closer to a year.
I can no longer login to the Wordpress dashboard. It bounces right back to the login page. I tried deleting my cache. I tried erasing all my cookies. I tried replacing the wp-login.php file. Nothing is working. Can someone please help me understand this sudden failure?
UPDATE----------
Looks like I am still on Wordpress 2.0.5