Had same problem. Hardware fault on the cover sensor - NOT missing magnet.

Fixed it with attached.

DISCLAIMER - READ FIRST AND CONSIDER: I am not a programmer; I like to tinker. YMMV.
My phone is running kernel-power49 - the module was compiled accordingly. I have no idea whether it will work with other kernels including the default (couldn't see any difference in the source but I can't guarantee it). Please don't blame me if it bricks your phone!

After messing about for hours editing and recompiling kernels, I discovered that you only need one module.

****Rename attached file to omap_hsmmc.ko (forum wouldn't let me attach without changing extension)****

Copy the file to /lib/modules/current (as root) on your N900. Also copy to /lib/modules/<name of your kernel> - in my case : /lib/modules/2.6.28.10-power49

NB: I'm not actually sure it needs to go in both but I did just to make sure. Perhaps someone more knowledgeable can advise.... ?

Reboot and VOILA: working mmc slot.

All I did was edit the source of the module to remove the cover checks. I only successfully completed this a few minutes ago but all seems well. I'll come back in a couple of days with an update.

It's a fairly crude hack and I might go back to it to see if it can be improved but I've spent far too much time recently farting around trying to keep this brilliant but seemingly delicate phone working adequately. I also have the communications error - currently fixed with some folded paper between the sim holder and battery.

Always greatly admired NOKIA stuff... never again!


Post taken from here:

http://discussions.europe.nokia.com/.../602757/page/2


Worked for me ok kp50 even it's compiled for kp49


Thx to howie99.

Reboot is needed