lol ...dir /s wont show em virus ..
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Try this dude .. 1st goto run and tyope "msconfig" then goto the startup tab .. and then remove all the unnecessary files // if its a r00tkit .. maby its not on that startup .. coz r00tkits and even hidden from task-manager ..
anyways after u remove that open task-manager and then goto process .. if u see any suspected file messing around End the file .. for example .. lest say "Ethical_world.exe" is a Trojan .. remove the Trojan with right click and "End Process"
There are some advance ways .. but I think this is inf for you .