Open regedit (Start > Run > type regedit and press ENTER)
Navigate to HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Common
Right-click, select New > Key and name it Graphics
Select the Graphics key you just created, right-click in the right panel and choose New > DWORD (32-bit) Value and name it DisableHardwareAcceleration.
Double-click the new value and assign it a value of 1.
Close regedit and try opening Outlook again.