Hi fixing this problem requires editing the registry. This can be very daunting for a novice and any mistakes can leave your PC unbootable. The other option is to reimage your PC from the disks that may of come with your system.
Did you get any disks with it? If not there should be an image on the PC. Do you have your book that came with it as it sould say where the image is and how to burn it to a dvd.
Here is the link for fixing the issue if you want to try it or better if you know someone that is good with editng the registry.
http://support.microsoft.com/kb/886549