A virus. I had wireless internet, and when I moved a "contractor" for my network, uninstalled my

Question

I had wireless internet, and when I moved a "contractor" for my network, uninstalled my antivirus program. As soon as he did this I believe i got a virus. My background says "warning:spyware detected on your computer. Install antivirus or spyware to remove it." It was in a file called antivirusxp08 which I cannot delete. I was told by his supervisor to reset my laptop to factory settings but I have no idea how to. Could maybe you tell me?