micro2440 LCD works for only few seconds on kernel 3.1

Hello,
I'm compiled the buildroot-2011.11 for a micro2440 in a main board with a 7
inches LCD, I selected to compile the kernel 3.1.4, compiling OK, download
on board OK, when it boots the Linux penguin appears but few secIonds
latter it disappears, the LCD turns off, the serial terminal OK too, and
when I ask to run an Qt demo application nothing appears, but when I press
the reset button the last application screen appears (in this case the Qt
demo). Whats wrong ? What the correct kernel configuration to LCD works ?

Thanks

You may have LCD backlight turned off. It is accessible via /sys. Try
echo 1 > /sys/class/leds/backlight/brightness
provided that you have /sys mounted.