Aug 18, 2010
[BUILD][17.08.2010][mattc Leo + Froyo w/Sense 1.5b][Kernel: huanyu 188.8.131.52 #6] – Page 250 – xda-developers
The same happend to me with quick settings widget. Fortunatelly I found an easy sollution. You have to connect your phone with PC and use adb:
adb shell “echo 255 >/sys/class/leds/lcd-backlight/brightness”
now the backlight is back and you can change the backlight brightness.