Once you have pressed the Power button on your computer, press the F8 key again and again. The Windows Advanced options screen such as the tart window normally will appear. Select the Last Known Good Configuration with the up arrow key.
Then hit enter. The concept of Last Known Good Configuration is to back up the latest settings of the machine. However, you can only use this function (1). If you do it more than once, you will not succeed. The window will pop up with Last Known Good Configuration and shut down before you can use this function again.