Won't stay logged in, even with "remember me" checked.

I was having this problem since Saturday.

I have Vista and use Internet Explorer 7. I deleted all cookies and temporary internet files, closed all browser windows, opened IE and logged into TPF again, closed my browser once more, and I was finally able to stay logged in.
 
I cleared my cookies and updated firefox and I don't stay logged in. I'm running Vista and Firefox 3.6. I'm not an expert and you've probably already checked this, but it seems like the session timeout variable may have gotten changed somehow to some really short period of time. That's the first thing I'd check anyway.