Re: [HELP] The light on my keyboard doesn't want to turn on
 

Unfortunately, if a reflash is not curing it - there is little else that can be done.

The above mentioned error when anything tries to access the /sys/ files which would normally be there indicate that the driver for the LEDs has not loaded.

This either means the software is somehow corrupt, or there is a hardware fault.
Unfortunately, it looks like - as it's persisted over flashing - it's a hardware fault.
You need to take your n900 in for repair.

Re: [HELP] The light on my keyboard doesn't want to turn on
 

Does the other LED work? (the one next to the display)

Re: [HELP] The light on my keyboard doesn't want to turn on
 

Now i notice that the other LED( it don't work when charging the phone) doesn't work . Does it help if i reflash eMMC ?

Re: [HELP] The light on my keyboard doesn't want to turn on
 

Afraid not, see what SpeedEvil said above.

Re: [HELP] The light on my keyboard doesn't want to turn on
 

I reflash the eMMC and the LED turn on again thank god )

Re: [HELP] The light on my keyboard doesn't want to turn on
 

Hmm, weird...
Any apps you installed lately?
No app should touch mce, unless it was lockdaemon (which I doubt since you reflashed)