If you cannot download and install anything then use a different computer to download a software called "malwarebytes" you can find it in google.

Then start your computer in "safe mode" and install malwarebytes using USB drive.

You can also view the follow thread

http://www.brighthub.com/computing/smb-security/articles/84717.aspx


Check out sajha thread on such free utilities http://sajha.com/sajha/html/defaultall.cfm?interestid=b7ab59c0-bb1c-445b-a2ea-129ea2685255&subinterestid=19