But it starts the clock. I have tried other buttons also but same thing.
Unfortunately, some cameras do not respond to the vers.req / ver.req shortcuts. You can use the Stick or CHIMP tools linked from
http://chdk.wikia.com/wiki/Bootable_SD_card to get the correct version.
You can also identify the firmware version from EXIF.
It appears that 500IS or 400IS both use the same version of CHDK, i.e 1.4.0.
Just to clarify, 1.4.0 is a
CHDK version. Every camera / Canon firmware requires it's own build, regardless of the CHDK version.
Not only that, even after I remove that SD, it still won't power up until I remove the battery and reinsert it.
That's because you tried to use an sx400 build on sx500. The camera crashes immediately, before any LEDs or anything are turned on, and stays hung until you pull the battery.
Find the firmware version of your camera and download the appropriate sx500 build.
