Slow logon, all of a sudden

Out of nowhere, my computer logs on very slowly, and
switching between users takes even longer. I've run virus
scans and ad aware scans, but nothing is showing up.

I also have been having "exceeded virtual memory" alerts
popping up for the past month or so.

Are these two related? If so, what do I do? If not, why
is my computer taking forever to log on?

Any help anyone has would be greatly appreciated.