Virus crippled my Computer! Help!

I encountered a nasty virus a few days ago that got past Norton 07' and my firewall. It did multiple things, such as disabling my sound and video codecs, as well as making security center forget I had Norton 07' and making Windows Defender crash everytime I tried to open it. After running a full scan of Norton, and a full scan of NOD32(downloaded trial) they both found nothing. I fixed the sound and my videos manually and thought that was the best I could do. But after returning home from class yesterday I found my computer in a deadful state. My computer will not start, and merely cycles through the boot sequence until it hits a blue screen of death. It starts up, and tells me Windows failed to load and might need to be repaired, giving me a list of options to select (safe mode, boot normal ect.) However the strangest thing of all is that my keyboard, or ANY keyboard, will not respond! I thought that perhaps the virus spread to the MBR and is preventing the keyboard from working. So I disconnected the hard-drive to tell the bios to boot from CD first. And the keyboard FAILS to work in the BIOS as well! But to my knowledge, it is impossible for a virus to infect the BIOS. I removed the battery on the motherboard for a full minute to see if that would cause the keyboard to function again, but alas it was futile. Since I'm trying USB keyboards, I thought to try PS/2 keyboards only to find out that my computer doesn't support them. So what should I do from here on out? Would buying a new HDD fix my problem? Or do I need to replace the motherboard?