Hi Ernest, I'm not sure what causes SU to stall or even crash but sometimes I also had problems when I imported DWG files "preserving drawing origin". Make sure to uncheck this in the Options dialog (open this from the Import window on nthe right) see attached image.. [image: jjZP_PreserveOrigin.jpg] If the original, CAD drawing origin is preserved, SU may import the drawing even some miles away from the SU origin which may cause OpenGL problems as well as you not seeing it in your viewport (press Shift+Z to zoom to extent and Edit > Select all to see if your drawing is somewhere "outer space"). Also, there are sometimes some small, stray lines very far from the origin or the drawing - zooming to extent and selecting all may let you see if there is such an issue again. Of course, I'm not sure if these are the problem but currently I cannot think of any other cause. It may be good if you could upload your file here.