Oh, I'm assuming XP. To fix it, enable the built in firewall, go online and download a removal tool. If it's an OS other than XP, you'll have to install new AV software to remove the virus, or go to another computer and download the removal tool from one of the anti-virus company's web sites.
Isn't it too late to start a firewall? From the way it's acting...it's getting to the black screen (where you press F@ to enter it)...then it stops and reboots again.....isn't that the registry? Would a firewall NOW help that? Just a guess on my part...maybe it's not the registry...
Oh, in more detail, to enable the built in firewall, open your connections (Start, Connect To, Show All Connections) in XP and right click on your internet connection and click on the advanced tab and check 'enable firewall.' Then go online and download a scan and remove tool. Run the tool and voila!