I agree with Arthur, FWIW. It only takes a few seconds to catch a virus or ruin some sectors of a harddisk. The latter can often be neutralized by reformatting (while reinstalling), but not always.

Obviously your Windows feels incomplete and cannot recover even with its self-repair mechanism (internal backup). Are you sure you don't have any CD, perhaps labeled "Recovery" or "System CD/DVD" etc.? Otherwise, as Arthur writes, call the place where you bought the machine.