Did you get a recovery disk with your computer? You may be able to use that to repair your installation, however the majority of systems come with an image disk, which has a "factory fresh" install - so you may lose any modifications / programs you have installed since buying the computer. If no recovery disks were with the computer, then it may be worth asking the manufacturer for them. Microsoft would only be worth trying if you have the original license for Windows XP (again, that should have come with the computer, but some, or rather most, don't).