Sounds like you'll need to boot from CD, fix the disc so it's functional again, then AGAIN boot from a CD, this time one with an Antivirus program on it, scrub the PC of all viruses, and then you *should* be good.
Something you clicked, though, infected you, so be cautious about mails from unknown sources, unknown websites, etc. My suggestion is that, after doing all this, you install the antivirus.