Here’s how you can start your Windows 10 PC in Command Prompt:

Power on your computer.

While powering on, press the appropriate keys on your keyboard to enter the BIOS.
Note: Different computers have different keys to enter the BIOS depending on their vendor. Most of the times, the correct key or key combination is displayed on the screen along with the vendor logo as soon as you power on the PC.

When the BIOS interface appears on the screen, go to the Boot tab.

Depending on the type of media you prefer to use to start the computer with, make the DVD or USB drive the first bootable device.
Note: The process to change the boot device priority may vary from computer to computer. The information about the correct keys to get this done is present somewhere on the boot device configuration screen itself.

• Insert or connect the Windows 10 bootable media (disc or USB drive) to the computer.
• Press F10 and then press Enter to save configuration and to restart the PC.

During the restart, when prompted, press any key on the keyboard to boot the computer with the bootable media.

• On the first window, select your preferred language, time and currency format, and keyboard layout and click Next.
• On the next window, click Repair your computer from the lower-left corner.
• From the Choose an option window, click Troubleshoot.
• Click Advanced options from the Troubleshoot window.
• When the Advanced options window opens, click Command Prompt.

On the command window, type D: and press Enter to go to the C: drive of your computer.
Note: Because your computer is started with bootable media, the System Reserved partition of your hard drive is temporarily marked as C: and therefore the C: drive that you see from within Windows 10 is marked as D: drive. This is a temporary modification. Things will go back to normal as soon as you start Windows 10 normally.
Note: Many commands can be executed when you are in the X:\Sources directory which is a temporary container that is created when you start Windows 10 externally. However, to execute main commands, it is important to switch to the system drive which in most cases is D: when the PC is booted externally, and C: when booted normally.

Once on the system drive, you can start typing and executing the commands as needed. After you are done troubleshooting, you can either type EXIT in the command window itself and press Enter, or click the Close button from the top-right corner to exit Command Prompt.

Back on the Choose an option window, click Continue to boot to Windows 10 normally. Alternatively, you can also click the Turn off your PC option if you wish to power off the computer and restart it any time later.