A: Check your layers. Sometimes the block is inserted on a layer that is frozen or turned off in your current viewport. Also, check your units; if your drawing is in Inches and the block is in Millimeters, you may need to scale it up significantly (factor of 25.4).
Start with a simple Frame & Brace block to test the quality, then expand into Cuplock and Ringlock systems. Happy drafting, and stay safe on those virtual platforms. Scaffolding Autocad Block Free-- Download