Just remove the line you added to the grub file and it should be the same as before.
I tried that man, i went through a lot of crap, driver and grub changes, updates etc etc.
The newest kernel still boots to a black screen, can't do anything. When i hold down the power button the screen comes on at the very last second just long enough that i see the shut down dialog.
The second newest kernel works perfectly, and after all my changes now allows me to adjust the brightness. So until i figure it out i'm at the mercy of waiting for the next kernel and hoping it all gets better.