Para começar, algumas dicas - a menos que você já tenha pago pela licença, eu realmente gostaria de comprar e instalar o Windows 7. Além disso, se a máquina estiver infectada com um vírus, eu pensaria em simplesmente fazer o backup de seus arquivos e instalá-los do zero.
Se, no entanto, eu não o tiver desestimulado (e novamente, eu realmente o recomendaria), eu seguiria as etapas que escrevi (e outras editadas) no
To get rid of them,
Start with a good tool such as Spybot Search and Destroy or Malwarebytes Anti Malware and perform a full scan.
After this has finished, use Microsoft / Sysinternals Autoruns and look through most of the tabs (you especially want to pay close attention to
Logon
andScheduled tasks
) and delete most of the items that you think are viruses or research them first.Next, protect your system with a good antivirus. I personally recommend Microsoft Security Essentials. You can also find a list of free antivirus solutions at this other question.
Also, it should be noted that some malware is very good at avoiding scanners, it is possible that once you are infected, it can install rootkits or similar to stay invisible. Sometimes, if things are really bad, the only option is to reinstall the operating system from scratch.
I personally do a few runs of Spybot Search and Destroy. If after 3 runs, it is unable to remove an infestation (and I fail to do it manually) I would go with a reinstall.