A Virus ...
Well...IF u have the Motherboard CD....there will be a Virus Guard in it...most Probably Norton..
Install that and Uninstall the existing Virus Guard U use for now...
(But not Sure this may help or not..But try...If i were U..I may have tried this..

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And then Check for Viruses..U'll get a list..then Delete them...
And go on Cleaning And Cleaning....that's the way u have to Follow...
or u can Simply Format the PC...But...why Format...this method helps out...
And if u couldn't Login ....Use Ubantu CD if u have...
