You can try by enabling the built in Administrator to disable everything in startup:
Step 1: To enable built-in administrator account follow these steps:
Insert the Windows 8 Disc.
Click on "Repair your Computer".
Click on "Advanced Startup Options".
Click on "Command Prompt."
Type: "net user administrator /active: yes" and hit "enter" on your keyboard
Now go Alt,Ctrl, Del 3 times and choose "startup" and disable everything there and reboot.
If it works then add back slowly until you find the culprit.
Note: Please follow the same steps and type net user administrator /active: no to disable admin account after the troubleshooting is done.