There is no switch on a desktop computer. What wireless network adapter are you using? One that is inside the computer (PCI card) or one that is a USB stick? Make/model? What happens when you try to connect? If there are error messages, please quote them exactly. Please also answer:
The First Question Of Troubleshooting: If the problem is new, what changed between the time things worked and the time they didn't?
The Second Question of Windows Troubleshooting: what is the malware/virus status of the machine? If you think it is clean, what programs (and versions) did you use to determine this?
Be sure the computer is clean:
http://www.elephantboycomputers.com/page2.html#Removing_Malware
MS-MVP - Elephant Boy Computers - Don't Panic!