Hey guys. I really need your help on this one. On my computer, I have Windows XP Professional installed, and was working fine until I decided to upgrade another computer to Windows XP using the Corporate version. Now that I have the second computer up and running, I head over to log in to my own computer and it gives me a Windows Product Activation Error saying "A problem is preventing Windows from accurately checking the license for this computer. Error code: 0x80004005" I licensed both installations to myself, and I think that's what's causing the problem. The Professional edition on my own computer was purchased and the license is valid. I can uninstall the Corporate edition if it will get my other computer working. I tried to contact Microsoft on the web, but it asks me for an product ID. Since I cannot get into my computer, I cannot get the ID, and therefore cannot provide it to them for help. Has anyone else encountered this problem or have a solution for it? Thanks in advance.