I think I need a little help.

I tried to update my SGS from I9000XXJF3 to I9000XXJF7.

I followed the steps with Odin etc etc....bu now my device does not reboot anymore! It only shows a white screen with blue letters "AT&T WORLD PHONE".

I can not get the device in download mode or recovery mode anymore. When I'm pushing volume down + home + on/off button, it shows the same white screen.

What can I do now? I hope I didn't brick the device....