[namtih]

@nj.raspi
Please try a more powerful power adapter with about 1A or more. Mobile phones often have such power adapters, perhaps you or friends have one lying around to test it before buying a new one.
You could also try to connect only the keyboard without the mouse.

@hidef
Please try to execute the following commands. Hopefully it will write a more helpful error message:

Terminal

sudo pkill xbmc.bin
sudo pkill splash
sudo /etc/init.d/xbmc start

@marke08
Please check this thread for more information:
http://forum.xbian.org/thread-66.html