When you load an assembly, each component will either be fully resolved or lightweight (1 - noted with a feather icon beside it) - To fully resolve an assembly, 2 - RMB at the main assembly, there will be an option to set lightweight parts to resolved.
SW Professional 2015 SP 5.0
SW Electrical 2D/3D SP 5.0
64 bit
Intel Xeon X(R) CPU 3600 @ 2.80 GHz
8.0 GB of RAM
NVIDIA Quadro 2000