As you don't mention any existing anti virus software I would suggest going to click here and getting Ultimate boot disk and the anti virus scanner, it's at the bottom of the download window. You will need two 3.5" floppies, the anti virus runs from the disk, but has to be used in conjunction with the boot disk, as it isn't a stand alone version. If this clears the virus , install an anti virus prog with a resident shield :- click here
click here or
click here . Then run whatever you choose again to double check the system.