something is getting in the way of the boot process.
you could try to
press F8 at boot to bring up the boot menu,
select:
Enable Boot Logging: This option turns on logging when the computer is started with any of the Safe Boot options except Last Known Good Configuration. The Boot Logging text is recorded in the Ntbtlog.txt file in the %SystemRoot% folder.
let it boot (and fail).
next restart the PC using the Last Known good, go open the Ntbtlog.txt file and look for something that says "failed" or something on the lines.
you should then be able to understand what is the component crashing the boot.
alternatively, if you recently installed a few apps, you could go in last known good, uninstall ALL of them and reboot. it MAY work, but your guess is as good as mine.
hope it helps,
N