Looking at the IXUS240/ELPH320 porting thread, it appears loading CHDK on that camera with the firmware update method is not reliable. link > Re: IXUS 240/ELPH 320 HS Porting thread
However, to your specific problem, you have to start the camera by pressing the Play button on the back lower right of the camera. Not the On/Off button. Then go immediately to the Canon menu and scroll down to the bottom.
And you really should try to get the "SD Card Lock" booting method working. Using the firmware update method quickly becomes tedious. Complete instructions are here : Prepare your SD card
, including a link to the CHIMP utility for Windows if STICK won't work for you.
FYI - most problems with STICK occur when people run on a MAC, or on Linux & Windows they don't use the starter script that elevates the privilege level for the actual java applet.