Hello,
I just bought an iMX53 QSB and I got a similar behavior.
I connected a screen on the VGA port, press PWR ON then the penguin appears on the top left corner of the screen while the kernel is booting, and when xorg starts, the screen becomes black.
On the serial terminal, the boot sequence seems OK, all gnome services are running, but nothing on the screen
I stopped Xorg and tried some basic applications based on framebuffer : on the terminal everything is OK, but still nothing on the screen!
I tried the u-boot bootcmd_obds command and I was abble to see the Freescale Logo on fullscreen, so (with the penguin at startup) I deduced that this shouldn't be an hardware problem...
Then I formatted the original SDcard and installed the linux image available on freescale => same behaviour
Then I tried the android prebuild image from Adeneo => same behaviour (on terminal android is OK, but nothing on the screen)
finally, I tried this very last Ubuntu 11.10 :
http://imxcommunity.org/group/imx53quickstartboard/forum/topics/newer-ubuntu-on-i-mx53-qsb
And I got Xorg working!
but I can't change the resolution (1024*768) and it's extremely slow!
Any clue?