So it sounds like I gotta install marlware bite software, scan computer with Comodo still on, and then if nothing is found, install SP3.
And the better option is to reformat the whole thing from scratch, which will 100% effectively kill all old files and viruses.
(I say 100% cautiously though, because with new ways to hack into a computer, who knows if a virus is capable of surviving a reformat.)
--I rather go with the first option, only cause I don't know how to do a fresh install of Windows XP with the software and all the stuff supposedly all stored in the hard drive(as I was told by the pawn shop owner).
I still question its effectiveness in completely removing all viruses, wouldn't a hacker good enough know how to corrupt the operating system file supposedly stored on this computer, and make it install his version of a corrputed Windows XP SP2?