Not sure about Win 8.1. I think you press F8 (Function Key 8 when the computer just starts to boot up, i.e. before any Windows stuff is loaded). This gives a menu of start up options (safe mode without network, with network, etc. etc.). The idea is that it only loads the essential bits of the software and hopefully not anything else, which is causing a conflict. Then you gradually add back the remaining functionality until you find the faulty application.
Have you just installed anything new, a game, new drivers, etc?
Grey Beard
