I am facing a bit trouble with Windows XP installation. My pc has face lots of virus issue due to which I was planing to format it completely. I tried a number of ways to wipe out the virus but it did not worked. Still there is huge number of trojan in the same. So I formatted the system and wiped out everything. When I install XP back again it is giving me issue with the license key. When I enter the key in that it is giving me error that the product id is not valid. It is not proper at all. What should I do. The key is exactly the same which I was using before.