Your PC has gone into repair mode because it thinks, rightly or wrongly, that part of the system has become corrupt. And it is hanging because either it can't find whats wrong or it can't fix it. Have you tried load a previous system that loaded? If so, I fear you may need to re-install your OS, but, if you have the current install disc, you may be able to re-install over the top and save all your settings etc.
HTC U12 Plus review: Hands-on