That could either be your hard drive is packing up or it could just be that Windows is stuck in a reboot loop. The reboot loop was quite common with Win XP and Win 7 but I haven't come across it on Win 8. With Xp or 7 it was just a matter of inserting the relevant installation disk and typing chkdsk -r at the checkdisk prompt. The -R or -r suffix told checkdisk to repair the Windows installation. Obviously you cannot do that with Win 8 or at least to my knowledge you cannot. I'm still going with the hard drive packing up idea but maybe someone else will come along with some other ideas.