HP Compaq NX6325 laptop wont boot and wont power of?

I was running Ubuntu Linux then decided to change back to Windows XP. I was happily running the Windows set-up disc to reformat the entire hard drive. After this was done, the set-up disc went on to copy over a load of files and then went into a reboot, the screen went black (OK) but then everything just hung . In the end I went to power off intending to start again. The computer would not power off except by my pulling out the battery and supply cable. If I reconnect the cable, I can power on with the power button after which I hear the fan and the optical drive being read but then it just stalls - nothing on the screen, cannot get in bios and still refuses to power off. It"s either a big coincidence or the three symptoms ( no screen: no bios: no power-off ) are all a result of the failure to self-reboot during the windows set-up? I have taken out the bios battery and left it out overnight but to no avail Can anyone help? Thanks
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