Need help getting rid of a virus!

I got a virus. At first it appeared when Microsoft Security Essentials found it and deleted it. Then it showed up again on the next scan and grew to two and four and more on each consecutive scan.

Next my desktop icons disappeared. I managed to find them and bring them back for a day or two while I worked to clean my computer of the virus. I tried to run disc cleanup but that disappeared from system. Next all my programs disappeared and now I can’t access the internet. I tried working in safe mode but I cant even find any of my programs. I tried to dump the computer and re-install XP but nothing works.