I do not see the Start button in Windows 8 but we can always go back to the old ways to restart Windows 8.

Press CTRL + ALT + DELETE keys all together.

You will see next scree where you can lock the desktop, switch users, sign-out and also open the task manager.

At the bottom right, you will see a little Power icon to restart Windows.

If you find any tips for Windows 8, please do share.

Cheers!