The best and the easiest way to tweak your computer is by using the Group Policy Editor. If you had opened it before, you'd be knowing that it is a wonderful tool for understanding the windows components because of the detailed description given for each key unlike the Registry. But suddenly, when you type gpedit.msc in your Run, an error pops up saying that it is disabled. Here are a couple of ways you can get your gpedit back to work.

Enable Gpedit from Registry:

1. Okay, this might not work for some versions of Windows but it is worth giving a try. Go to Start --> Run and type regedit followed by the Return key. 
2. When the Registry opens, navigate to the following key
   

   HKEY_CURRENT_USER\Software\Policies\Microsoft\MMC

   Check for the key RestrictToPermittedSnapins and set it to 0. This would remove the restrictions assigned to it. If you're planning to disable it, you can select the value as 1.
3. Now reboot your computer for the changes to take effect. Check if its working. If not, you'll need to move down to the other methods.

Using Registry and MMC:

1. Open the Registry by typing regedit in the Run box. 
2. Navigate to the following location
   

   HKEY_CLASSES_ROOT\.msc

   Now check and delete any key present on the right-side except the Default key.
3. After that, restart your computer and type gpedit.msc in the Run box. Group Policy Editor would ask you which file you'd like to open it with. Then select the Browse button and select mmc.exe from C:\Windows\system32\. 
4. The next time you type gpedit.msc in Run, you'll be able to see it working.

Using Microsoft Management Console(MMC):

1. Go to Start --> Run and type mmc.exe to open your Microsoft Management Console application. 
2. Now go to File --> Add or Remove Snap-in. A box would open in which you'll have to select the Add option below the Description box. 
3. A long list of Windows applications appear from which you're supposed to select Group Policy Object Editor and you'll have it running in that console.
4. Save the console in any place you want so that you can get it to work with just a Double-click!

Using the Command Prompt:

1. Go to Start --> Run and type cmd to open the Command Prompt. 
2. If you've come this far and still dint get your Gpedit working, that should mean the dlls associated with the Gpedit in your system are somehow unregistered. So you'll have to register these dlls.
3. In the Command Prompt, type the following commands to register them
   * regsvr32 gpedit.dll
   * regsvr32 fde.dll
   * regsvr32 gptext.dll
   * regsvr32 appmgr.dll
   * regsvr32 fdeploy.dll
4. Now type in gpedit.msc and you'll see it working.

If neither of these methods work on your computer, it means that gpedit.msc is deleted from it. So you'll have to install it in your computer. To do that, download the file GPedit.rar, extract it to a folder and run InstallGPEdit.bat for auto-installation of GPEdit.msc.