oh there was indeed something wrong with the modules.

lib symlinks to usr/lib. I broke that somehow when I did

yeah and I followed the elinux/n900 page too blindly for compiling the kernel/dt kernel. did both. so the modules didn't get the correct config values (I guess..)

the watchdog hint was the key! thanks

I can log in now and there is no shutting off anymore but lots of services are failing. including logind. but I'm onto that.