It may be the old problem that is reoccurring. I don't get it often but it has been happening most of today for me. Shows you as not logged in but you are. I was chatting in sb earlier which you cannot do when not logged in, glanced up and it showed me as logged out so I just tend to press F5 to refresh the page, usually works after one or two attempts.
When you initially went in to your profile, did you attempt anything like posting or chatting in shoutbox. If you can do either you are logged in and possibly just need to refresh the page a few times.
I will probably be cleaning my cache tomorrow using ccleaner. You may want to try that too. If so you can get free download here.