I wanted to upgrade my operating system on Lenovo ThinkPad T400. For upgrading I have successfully installed Microsoft XP operating system on it. After successful installation of windows operating system there is a problem with my Lenovo ThinkPad T400. When I start the system it won’t boot. I also tried to remove the hard disk and connect it into the USB port of the system. After connecting hard disk into the USB port I restarted the system. I am facing the same problem of booting. I want a solution to troubleshoot booting problem.