It is possible that the OS is applying updates. By this time there are quite a few. With many of these, which require turning off services, an automatic reboot is applied. If you can get into your computer, between the updates, go into the Control Panel - Updates and, temporarily, turn them off. Also, whilst there, look to see what updates are pending.
To be honest upgrading from xp is probably not the best road to go down. Have you considered performing a clean install?
We see many posts from users who have upgraded and the usual solution is to perform a clean install.
hi Dave, I always run windows update prior to attempting the upgrade,it is when the upgrade completes that the system tries to reboot,but does not achieve this