Screen flickering in Windows is usually caused by display drivers. I shall suggest you to uninstall the graphic card driver in Safe mode. Reboot. The OS will detect the driver automatically.
Power on your computer.
As soon as the manufacturer's logo appears, press and hold the power button until your PC shuts off.
Again, press the power button and repeat step two.
After 2-3 attempts, your computer will boot into the blue screen with various options.
Here, click on Troubleshoot > Advanced options > Startup Repair.
Choose the user account, enter the password, and click on Continue to begin Startup Repair.
After Startup Repair completes its job, reboot your computer and try booting into Safe Mode again.