Don't you just hate it when Windows 8 refuses to start up because of some error you have no idea about. The common errors include the one shown above which doesn't exactly tell you what to other then sacrificing your data and re-installing the Windows. Before you do that, Microsoft suggests, a person should try its new "Refresh Your PC" or "Reset Your PC" options that come in-built with UEFI boot mode in Windows 8. But they are not fool-proof and more often then not end up giving errors like "The Drive where Windows is installed is locked. Unlock the drive and try again." or "Unable to reset your PC. A required drive partition is missing."
If you are getting these kind of errors, then chances are you have a corrupt MBR (Master Boot Record) or BCD (Coot Configuration Data). Doing the following steps can help resolve the error. Lets have a look at them.
Note: You need installation media for the respective version of Windows 8 running on your machine.
Step 1: Insert your Windows 8 Installation media and boot the computer through this.
Step 2: You need to get to the command prompt. To do that, Select your language when it asks and click Next. Then, on the screen, click on the link in the lower left corner that says Repair your Computer. Then on the next screen, Choose an Option screen, click on Troubleshoot. In the next screen, click on Advanced Options and now you will be able to see a Command Prompt button. Click on it.
Step 3: You need to input and execute (press Enter after typing each one) three commands in the command prompt now.
Command 1: bootrec /fixmbr
Command 2: bootrec /fixboot
Command 3: bootrec /RebuildBcd
Step 4: After you execute Command 3, it will ask you to choose an option between Y (Yes), N (No) and A (All). Type Y and press Enter.
Step 5: Type Exit and click Enter to exit the command prompt. Remove the disc and try booting again.
This should solve the problem you have at your hand.