Follow these steps
1
Disconnect unnecessary USB devices and restart the computer.
2
Enter Windows Recovery Environment by interrupting startup three times or using a Windows USB.
3
Choose Troubleshoot > Advanced options > Startup Repair first.
4
If Startup Repair fails, open Command Prompt in Recovery and run: sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows.
5
Use System Restore if a recent restore point exists.
6
Avoid reinstalling Windows until you have backed up recoverable files.