Ray Gomez, a detail engineer, shared this tip that will help you avoid trouble with unresponsive AutoCAD drawings:

When working with 3D solids, sometimes a drawing will be very sluggish, not respond, and eventually freeze, so I have to force AutoCAD to close. I have found that having the DISPSILH command (controlling the display of silhouette edges of 3D solid objects) set to 1 will cause this. By turning the command to 0, it is then possible to work on the drawing without any lockups.

Notes from Cadalyst tip reviewer R.K. McSwain: This is another good example of using one of the hundreds of AutoCAD system variables to help a particular situation. Ray has found that by turning this sysvar off, his stability and speed are increased. Specifically, DISPSILH controls the display of silhouette edges of 3D solid objects in a 2D wireframe or 3D wireframe visual style. A value of 0 tells AutoCAD to not display the silhouette edges, and changes to this variable will require a Regen.