To restore the operating system of a Nova II, hold down part edit button 6 while you turn the synthesiser on. The display will show "reload O/S from ROM to flash?". Push the page up button to accept this prompt. The reload should take around 5 seconds.
Once the reload is complete you can restore the factory settings. To do this find the local control & memory protect page in the global menu. Ensure that local control is turned on and memory protect is turned off. Press the page up button to advance to the restore from ROM page of the global menu. Use the fast data controls to select "total data" as the option to be restored.
Push the write button twice to initiate the reload. This reload takes around 15 seconds. Once the reload has taken place, the memory (not the buffers) will have been initialised. Turn the Nova II off and back on again or advance to a new Program / Performance to clear the buffers. The items that are restored are: Program banks A-D, Performance banks A-B, Drum Banks a-d (Supernova II only), all arp patterns and the global menu data. Program banks E-H.