Where did my texture go after selecting Use Nodes? I created a material for the Cube


Color map
Normal map

Unwrapped it
Enjoyed the view in the viewport with Internal and the Game Engine
Then I switched to Cycles and clicked on Use nodes and there is no more texture in the viewport of Internal and Game Engine


What happened? Can I undo that somehow? I read that Cycles's is not compatible with Internal.
Can I have materials set for Internal/GE and Cycles and switch between them (the rendering engines)?

I intend to export my creations to my own game engine and eventually to render still images for enjoyment but the former is what I need most.
Materials created for Blender Internal are not compatible with Cycles. Blender Internal uses an entirely different nodes system, stemming from the fact that it is an entirely different rendering engine and rendering images via an entirely different method.

To use your texture in Cycles, you would need to recreate your texture in Cycles, or otherwise use a script to convert it to Cycles. See this answer for more information.