I'm new to Creo and have just begun assembling parts. The problem is when I try to create a part in Assembly Mode they always appear hollowed out. For example if I were to create a simple cube, the cube would be missing it's centre completely. This doesn't happy when working in Part Mode, everything is solid. Does anyone know what settings need to be changed to rectify this
One of two things are happening. 1st check that you activated the part in the assembly and you are indeed creating the new feature in the part, not in the assembly (right click on the par tin the tree and "activate"). Then it should behave pretty much like you were in part mode.
You have 3 options with extrude. Solid; thick, or surface. For some reason, you are either getting a surface or a thickness depending on the color when you accept the feature. Gray means solid, and shiny blue-ish means surface.
But... if you are creating an extrude in the assembly (assembly is active), then you have limitations. You cannot create solid features in the assembly. You can make cuts... but not solids. You can also create surfaces in assembly mode. The purpose for solid extrudes in assembly mode are to remove material only.
Hope that helps, and if not, please feel free to add images to make clear what you are seeing on the screen.