Virus on your Computer ?

Then i would recomment to download a 60 day trial version of
Norton Internet Security 2011
,install it,update it and scan the PC afterwards with the integrated 'Scan Now' feature.
http://www.pcwelt.de/downloads/Anzeige-Norton-Internet-Security-2011-586871.html
If your partitions are containing any cracks,keygens etc,safe them to disk before even touching Norton,or he will likely delete them.:)

You should deinstall Norton after the trial period only with the
http://www.nortonremovaltool.org/
again.
Then restart the computer and install NIS for another 60 days right again with the privious described process.:)
P.s.:
We keep of course all installers of downloaded software well sorted in a seperate folder from where we can install anything right away.Our software collection is quite large,by the way.:)