I have problem were my sons pc has died a death from a virus

which ran when the pc was restarted ,AVG spotted it and removed it but it seems it also took some system files with it.

Know it will start to boot into windows but then go into a loop of rebooting.Also if I go into the start options or the BIOS options the image is not readable. Can I get hold of a virus boot disk that will run straight from start up and hopefully with the minimum of options because i cant see the writing on the screen.
The good news it keeps him of the chat for now.
Thanks in advance.