Your machine has touch enabled or a mouse with a scroll wheel.
In the Windows 8 Start Screen, you have a horizontal scroll bar.
You use the touch function to flick back and forth or use the wheel on the mouse to scroll back and forth quickly.
Sometimes, the horizontal scroll bar may freeze and you can no longer scroll in the Windows 8 Start Screen. And if you click, the click location is different from the cursor location.
This is a timing issue within Explorer.exe while it is trying to process a large number of scrolling or flicking commands.
Please choose one of the following options to mitigate this issue:
Press the "Windows" key to jump off the Start Screen.
Switch to any apps opened at that time.
Activate the Charms menu and jump to any other page.
After any of the actions above, you can access the Windows 8 Start Screen again and the horizontal scroll bar will work again.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.