What other OS are you trying?
From a fresh install, of any Raspbian image.
rpi-update and editing
/boot/config should work.
Even after doing this... it will "look" like it isn't working as the screen will still be black. You need to tell the Raspberry Pi to start using this screen.
If you see /dev/fb1. then the drivers have loaded.
After following the instructions in my last post.. did you perform the quick test the bottom of this page;
This quick test should display a picture.
If the test works, and you would like X to appear on PiScreen.. then follow this;
Or.. to enable the console;
Mark --OzzMaker.com --