It's really weird, but sometimes computers can do that because they just store too much shit on their hard drive and the windows startup can't load properly because of some tiny discrepancy in what's written onto the drive.
If you can actually get the computer to start up again, it's easy to fix to prevent it from happening again. Anyone can do this on their computers to prevent something similar from happening. All you have to do is go into your C:/Windows folder, and find the folder in that called "system 32" and just delete it, then restart. This will clear out all the temporary junk files you don't need any more, but windows keeps anyway. Try it out