This is a total longshot...(translation=I have no idea), do you use any kind of registry clean-up program? If so, try restoring the registry to the last known good backup.
I'm guessing by your last post you have security programs preventing virii etc. Could try something different, like
http://www.ewido.net/en/ (30 day free trial) which picks up stuff, including trojans, some of the others don't.
Guess you'd have to download that on another computer and transfer it to yours.
There must be something you can do short of having to reinstall, but that might be the only option. This sounds weird.
What was the nature of the last item succesfully downloaded? Could it, or anything else, have wreaked this sort of havoc?
Do kids have access to the laptop? Very destructive.