Samsung Galaxy S 2 doesn't switch on or go into download mode , yellow triangle with exclamation mark
Well... you have experienced a soft brick!

You did some thing you didn't need to do, but it's not the end of the world and you can fix it.


You flashed an ICS kernel on a GB device - big NO NO,
ICS kernel goes to ICS ROM only
You used Odin 3 when you should have used 1.8


So, how to fix this?

Download speedmod kernel for I9100 (i prefer his work) from this
site and flash using the correct Odin version

If, as you said, cannot go into download mode you need to get a JIG that will force your device to go to download mode (you have to go into download mode or you can't fix it)

By the way, can you go to recovery? VOL UP + HOME + POWER?