Sounds like a pretty simple case of some corrupted cookie files. Also possible you installed some kind of security related add-on to the browser recently, and that's part of the problem. Good place to start, is comparing every difference between the browser on the computer that works and the same browser on the computer that doesn't work. You can also download a second, or third, web browser for the computer not working. If that one lets you log in properly, then your issue is with the browser config. If not then you probably installed some new AV program or something that is screwing up your access.
Recently been having trouble logging in to like Yahoo, or eBay or even one of my own Forum boards.
Like I just tried to log in to a board and it said I had specified in incorrect username or password.
Went to another computer on my little home network and logged in without any trouble.
Numerous instances like that.
I think it must be my computer and not a virus - I've run many checks - something else. What? Is there some part of XP that can fail in that manner?
Does anyone have any clues on this?