This is strange i just shut down my n900 again and it shuts down the os, it gives me the nokia logo with usb logo top right. then the screen goes complete black and the LED stops flashing. I then get the message from my PC that the n900 is connected via mass storage i can then browse my files on my n900. Dont remember i got this in the past..

@ fargus the phone starts without the charger so i think it has enough power. the power failure could be a problem. but it indicates charging fine when n900 is on. i will try to charge when device is off with the normal power charger and see what happens then.

Thanks for all the replies!