Have you tried safe mode?
Too many potential causes to hazard a guess, but the preventative measure, already too late if it's not already done, is backup.
I backup my OS every time there are significant changes to configuration or large updates. Restore points are just not robust enough to rely upon, and they take up space.
Start with safe mode, and let us know if it boots further than normal mode. If not, you're basically locked out of the OS. It may be faster to re-install, or, of course, restore from backup if that's available, than to diagnose.