It's something which you've uninstalled or partially installed which Windows is calling for during the boot process, but which is not kicking in as Windows expects - therfore causing Windows to stop loading.
You can call it malware, or your can call it software. It's something you've permitted to install improperly or which you've uninstalled improperly.
A delve into your msconfig.exe interface might provide clues.
A good registry cleaner might correct broken pathways.
Thinking about what you've done since the prior clean reboot is also a sound idea.
Use system restore to rollback to a moment when your core startup files worked properly, or better still restore your ghost/acronis drive image.
You do make back-up's don't you?!?!