@Tania_Hernandez: From my test running Insync in Ubuntu 16.04 for the first time will result in Insync using a lot of CPU for a few minutes during which period the tray icon will not show. But after that period has passed Insync will execute normally. Subsequent runs would also be normal. Please check if waiting for Insync will work in your case.
Also please send the output of the commands cat /etc/apt/sources.list and cat /etc/apt/sources.list.d/insync.list to confirm the Insync entries for your apt repo.