It sounds like your computer got set to a high resolution that your monitor will not support. It may also happen if it’s really low like 640x480. It can also be a case of your refresh rate being set to high as well. It’s hard to tell if its Windows related without seeing how far the boot process goes. If you can get into Safe Mode then you can turn down the resolution and refresh rate. You should be safe at 800x600. If you can’t get into regular Safe Mode then try Enable VGA Mode.
If you get in then right click your desktop and choose properties. Go to the Settings tab and adjust the slider to 800x600. Then click on Advanced and go to the Monitor tab. Under Screen refresh rate set it to a medium setting such as 60 Hertz. Then reboot your computer and see if it will start in normal mode.
There may also be a chance that your video card is having problems and may need to be replaced. You can also test by hooking up your computer to a different monitor and see if you get the same results.