Screen going black with power saving disabled

Greetings,

I have disabled power saving features in linaro ubuntu 11.10 on a PandaBoard, in order to prevent the screen going black, since there is no mouse nor keyboard attached to the board (It is simply displaying videos, in a closed loop). But when I reboot (Or power up after a time with the board off) sometimes this works, and sometimes not. There seems not to be any kind of rule for it to work, it can fail 5 or 6 times (going black after 10 minutes, even when it is set to "never"), and later work ok for 3 or 4 reboots. And then, fail again.

Can anyone enlighten me a bit? Sorry for the joke, but my brain is almost as dark as black the screen goes...

thanks in advance,