run hijack this on the pc available for download from http://www.spywareinfo.com/~merijn/programs.php

this shows you what processes are running on your system

select the option to create a log file and then paste the results into this website
http://www.hijackthis.de/

That website will then tell you what is hijacking your system and identify suspect files causing pop ups along with dispaly the virus running.. you can disable all these issues using Hijack this itself and then run a virus scan of the system and all should be reasonable. The following URL is a free online AV scan

http://housecall.trendmicro.com/uk/

Or you can paste the log file here and I will tell you what to loose, formatting a PC is a last resort imho

ive not formatted for 3 years and do not have any anti-virus, anti-spyware or pop up killers at all