Start your PC then just as Windows loads - press and hold Power Button for 5 - 10 seconds to perform a shut down. Do it 3 times. You may only need to do it twice, but on the third start Windows will boot into the recovery environment.
You can also hold shift > press restart in the start menu to do the same
1:
Go to Troubleshoot > Advanced Option > Startup Repair
This will try to make Windows repair itself.
Error: NTLDR or NTDETECT.COM Not Found when starting Windows