To enable registry editor that was disabled by some malware please do the following to regain access and perform maintenance:

Enable Registry Editor using Group Policy Editor 
1. Click on the Start > Run and type ”gpedit.msc” on the field (without “).
2. Navigate to:
- User Configuration
- Administrative Templates-
- System.

3. On the option: Prevent access to registry editing tools
4. Click Disabled and click on the OK button to save settings.
5. Reboot your computer.

Enable Registry Editor Using Free Tool
RRT or Remove Restrictions Tool is a free tool to enable access to different Windows process disbaled by virus infections.

This tool is used to enable access to:
- Registry Tools (regedit)
- Ctrl+Alt+Del
- Folder Options
- Show Hidden Files

Download RRT: click here to donwload

Enable Registry Editor Using Registry Keys
If the above procedure does not work. You may also use a tool to reset registry keys here. Make sure to backup your registry before making any changes.