I posted this last week and forgot to attach the file and after I attached it I didn't get any answers.
I'm sorry guys, I know I am always asking questions here, perhaps some are really basic, however, my thesis is due next month and, as it seems, my knowledge with NX10 was worse than I thought so and I am going a little insane. I have a part that had a 2mm thickness and I used 3D elements, but I was adviced to use 2D. So as I did (or tried to) all of the meshing seemed to be off. So I tried to redo it and everytime I do a simple Eigenmode simulation, I lots of 0 hz modes, meaning parts are disconnected from the rest of the assembly. Can you look at the files attached (the .fem file and the idealized part) and maybe redo the meshes or simply tell me what did I do wrong?