My ultrabook returned from repair with replaced HDD. I've activated the OS using Microsoft's automated phone authentication. All was fine till I wanted to factory reset the system. Everytime I try to do I get a prompt saying that some files are missing and I should use a Windows Recovery disc/USB. Of course no such thing is in my possession and the only way to have a clean Win 8 is through factory reset option. Any suggestions. Maybe updating to 8.1 will solve the problem?