Win8 can't load the operating system when it starts because the digital signature of the file can't be verified.

This is because an error occurred while updating the driver, and the signed driver cannot be updated.

See if you can enter safe mode, and if so, set not to use signature driver. The steps are as follows:

① Shake the mouse in the upper right corner of the screen to pop up the charm menu → Settings.

② You can also press Win+i directly to open the setting interface, and then click the bottom to change the computer setting options.

③ Update Recovery → Recovery → Advanced Start (restart immediately)

④ Select an option → Click the troubleshooting option.

⑤ Select Windows startup settings in the advanced options, and continue to click Restart.

⑥ Start Setup → Select Disable Driver Mandatory Signature (or press F7) to restart the computer.

⑧ Click the option to disable driver forced signature in the selection menu, and then restart the computer.

Note: The operation menu of Windows 8 operating system is slightly different:

Click the General menu in the Settings tab on the left, and then click Start Now on the right to restart your computer.