Can anybody tell me what would make my performances disappear? I have 4 saved in memory, and 1 and 2 stayed intact but 3 and 4 suddenly went back to the factory settings. And, once I fix it, how can I save it to the disk to avoid losing it again?

Really weird! Patches and Performances do not usually disappear once saved (using the disk/utility\1:write function). Anyway, saving to disk is as easy as pressing disk/utility then 3:save and then 4:sound. This is the way you save not only a patch or a performance but a whole user bank. To load it later press disk/utility then 2:load then 4:sound. I usually also save my user banks using Change it! (a wonderful JV/XP freeware editor) or even the Studio Module of Cubase. In order to do this you obviously need a computer and a MIDI connection.