I have in my device error 0c000021a, how can i fix it?

Un-plug all the external devices connected to the computer, except mouse and keyboard and check if the issue is resolved.

Try these steps and let us know the results.

Method 1: Boot into Safe Mode.

Boot into safe mode using the Windows 8 DVD/installation media. If you don’t have a Windows 8 DVD, refer to the following link to do so:

How to create installation media for a PC refresh or reset

http://windows.microsoft.com/en-US/windows-8/create-reset-refresh-media

Now, using the installation, let us boot Windows in safe mode.

a. Boot from Windows 8 DVD.

b. After you see a Choose an Option, click on ‘Troubleshoot’.

c. Now click on ‘Advanced Options’ and then on ‘Windows Startup Settings’.

d. Use your arrow keys to go to ‘Safe Mode’ and hit Enter.

Check if the issue occurs in safe mode.

Method 2: If you are unable to boot into safe mode, then follow the steps below to perform Automatic Repair.

a. Boot the computer using the Windows 8 bootable DVD.

b. On the ‘Windows Setup’ wizard click on ‘Next’ and click on ‘Repair your computer’.

c. You will then see a blue screen and an option to choose.

d. Click on ‘Troubleshoot’ then click on ‘Advanced Option’ and then click on ‘Automatic Repair’.

If you can boot into safe mode, perform System Restore.

Method 3: Boot from the Windows 8 DVD and then perform system restore and check if it helps.

Follow the steps to perform system restore:

a. Insert DVD and press F12 key and click on Change Default or other options which is at the bottom of the screen.

b. In the next screen click on TROUBLESHOOT option, this will display you different WinRE (Windows Recovery Environment) Options to resolve issues with the computer when it is in no boot state.

c. Now Click on System Restore, this will open up a Wizard and restore to a point when the computer was working fine.