When Windows 8 fails to complete updates, there could be a number of reasons. There could be an internet connection problem, low disk space, Server issues ,a software conflict, or corrupted system files, Shutting down or restarting the computer during an update. To resolve this problem,restart your computer and then check your internet connection,run Disk Cleanup, unplug non-essential USB devices. you can also clear the update cache, and then restarting the services or running the Windows Update Troubleshooter.