Vivo,
Weird things on screen usually indicate a display driver problem. Firs check that your graphics card settings are set to the SU-recommended values. If that doesn't help, you can, as a diagnostic test, try turning off Hardware Acceleration in the Window>Preferences>OpenGL dialog.
If that helps (it has the side effect of making SU run much more slowly) you should go to your graphics card's chipset manufacturer's website (usually Nvidia or ATI) and download and install a newer (or different) version of the graphics card driver software. You might have to try different versions before a working one is found. Running SU with Hardware Acceleration off is a viable option only if your models are very small.
Anssi
