Having issues with logging into your copy of Windows 8 or 8.1, you can try the following to fix the issue.

Run chkdsk /r on your boot drive and your other partitions, you will need to boot to a Recovery CD or USB and get into the command prompt to do this.

Still not working, run sfc /scannow from the same command prompt.

Repairing the EFI Bootloader in Windows 8

If all else fail’s, follow this link