Hi,
Please do try these troubleshooting steps that may help in solving the issue.
- Start by doing a hard reboot, remove the battery and unplug the AC adapter then press and hold the power button for 20 seconds then try if it would boot up normally to the login screen.
- If these doesn't work do try to run it in Safe Mode, while the laptop is booting up repeatedly press on F8 until it loads Advanced Boot Options select Safe Mode and see if the login screen will appear.
- If it will load in Safe Mode first to do is to run System Restore, restore it back to an earlier date or time before the problem happened.
- If it would also not load in Safe Mode last option would be to reinstall Windows itself.