You restaritng pc must have damaged ongoing windows update installation. If you encounter it again just suffer through a lot of waiting, trust me I once started update process before going to bed and in the morning it was still rolling until finally ended in the afternoon.
Now about the fix first thing you should try is getting to windows recovery options (windows 7) or advanced startup repair (windows 8&10) by pressing one of the F keys (F4,F8,F11 etc.) while booting the system, which one depends on your system so try it out. The you'll have to choose system repair or startup repair, note that even when sometimes its says it didn't do anything or failed the repair it might have actually kicked in.
If that won't do the trick second...