I went through this with my CT322. If it is not a safety sensor or a bad control panel, then there is a lock code that will disable the machine. If the previous owner did not change the code you can try these. Mine were changed and the dealer had to replace the control panel.
Default unlock codes-3 tries then need to turn key off/on to start again
000 , 998 or 999
00000, 00998, 00999