2 – Choose a different viewport
If you can’t still see the textures after this, please make sure you are Not using viewport2. Mentalray and viewport2 sometimes don’t work properly together (Maya 2014 and 2015).
3 – Locate Properly the textures
If it still doesn’t show the textures, open the Hypershade window (window->rendering editors->hypershade) and once there you can change where to find the texture by selecting the texture and changing the location in the “image Name” you can find in the “File Atributes”. The textures will always be placed somewhere like this: /installationfolder/sourceimages/assetname/texturename.jpg