I have the problem that my blender hasn't updated correctly and is stuck on version 2.78 while it says that it has version 2.79, the issue is that I'm missing nodes like image textures and diffuse BSDF and the whole shaders option in the 'Add node' menu.
There are three possible causes;
1- The render engine might set to Blender Render (also known as Blender Internal) instead of Cycles. Materials work very differently in each of the render engines, and are not interchangeable.
Blender internal does not use shaders, Cycles does.
2- The node editor might be set to a different mode.
There are three different modes for the node editor and they use different kinds of nodes.
Change to the Material node editor (and make sure that the Use Nodes box is enabled).
3- If Cycles is not available in the render engine list, then it needs to be enabled in the System Preferences>Addon List (Access the system Preferences window by pressing CtrlAltU)
Look for the Cycles Addon in the render section, enable it using the check box and then save the user settings to enable cycles permanently.