Try starting it up in "Safe Mode" and see if it will fully load. Granted you will have limited access, but if it loads, then you know there is a software problem. Bad program, virus, malware, etc. that you need to fix/remove. Now if it still won't load in "Safe Mode" either then it could be the OS needs to be reinstalled, or there is a hardware issue.
How to enter "Safe Mode" when booting the computer.
In Windows 8 and 10...
As your computer restarts, press F8 (possibly a few times) to enter "Safe Mode"
a. Press the "F4" key to Enable "Safe Mode".
(The computer will then start in "Safe Mode" with a minimal set of drivers and services.)
b. Press the "F5" key to Enable "Safe Mode" with Networking.
( Once "Safe Mode" with Networking...