Samsung Galaxy S 2 doesn't switch on or go into download mode , yellow triangle with exclamation mark I had Galaxy S2 with Gingerbread kernel, I needed to upgrade it to ICS. I used Odin 3 v3.04 to download the ICS kernel (I9100) to the phone. I followed the following steps:


You start with the phone disconnected from the computer and switched off.
Start the SGS2 in download mode: you do this by pressing "Volume down", the "Home" button and the "Power" button at the same time. Don’t release them until the download mode screen appears (it looks totally different from the normal starting screen).
Follow the on-screen instructions: 'Continue' by pressing "Volume up".
Start Odin 3 on your computer.
Click on PDA and select the tar-archive containing the kernel you want to install.
DO ONLY check the option boxes "Auto Reboot" and "F. Reset Time".
Connect the SGS2 to the PC via USB. The first field of "ID:COM" should turn yellow stating the COM Port of your device. Continue only after this has happened. It can take a couple of seconds.
Click Start and wait for the flashing process to finish. 
After that it said "Reset", and I powered off the phone


10.When I switched on the phone Odin said Pass 

*But now I have a yellow triangle with an exclamation mark in the middle, no switch on happening, not able to get into download mode also.*
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?