System Low on Virtual Memory

I have a Dimension 4600C that was purchased in August. For the past two days my entire system is running slow, every program.  I am connected to a LAN and every so often i get a message saying that I am running low on virtual memory. Also, my programs have began to freeze alot and i have to restart alot. The fonts on webpages I access are smaller than usual. Sometimes my keyboard will stop working and I have to restart my system. Also when my computer trys to return from the screensave, it will just be a plain black screen, and I have to Ctrl-Alt-Del to get back to my desktop. I am not sure if all of these problems are connected but they all just started yesterday.  Also, my operating system is XP Home. Thanks in advance for any help you can offer.

ZacHawney