1
Are you able to force your PC into the recovery environment using these steps.
Start your PC, just as Windows attempts to load (spinning dots), press and hold Power Button for 5 - 10 seconds to perform a Hard Shut Down
Do this twice
On the third start Windows will boot into the Recovery Environment and from there you can access System Repair, Safe Mode, Command Prompt... etc.
2
If that process does not get you into the Recovery Environment, what is the make (Dell, Asus, Lenovo... etc.) of your PC or motherboard.