Hi,
You said that pressing F8 has no effect...may be the Worm Effect...
Anyway, get a DOS bootable and boot through it and remove the Worm Files. And be sure to replace them as said by other members.
Have you tried Stinger 2.4.3 (Released on 29/OCT/2004)
http://vil.nai.com/vil/stinger
Hope this helps!
Bye!
GA