We should note first that you can always get to the run dialog by just hitting Win + R on the keyboard, which is the simplest way to do so, and would probably be worth getting used to.
Otherwise, you can re-enable the run dialog by right-clicking on the Start Button, selecting Properties, and then clicking Customize on the ensuing dialog window.
You’ll be taken to the Customize Start Menu screen.
Check the “Run command” checkbox in the list, and you should now be in business:.
Note the addition of the Run… button.
