The IE10 Metro App permanently disables if IE is not the default web browser on your computer.  If you change your default Web Browser in the "Default Programs" Control Panel applet to something other than Internet Explorer 10, then the Start tile for Internet Explorer will automatically default to the desktop version of IE10. The only way to get the Metro IE10 App back is to set Internet Explorer as your default web browser.
To do this,

  1. Click Start.
  2. Search for "Default Programs" and launch the applet.
  3. Highlight Internet Explorer and choose Set this program as default.
  4. Close the Set Default Programs window and go back to Start.

The Internet Explorer 10 Metro App should be present in Start. If not,

  1. Click Start.
  2. Search for Internet Explorer.
  3. Right-click Internet Explorer and choose Pin to Start.
  • Joe