I re-seatted the card many times now. And also clean the card. Formatted it to Fat32 using -Quick format on WIndows7. But still not showing up. The memory card work on other phone though.
Might be worth checking the output of dmesg command in xterminal, shortly after you put the back cover back on after inserting the card. Look for stuff to do with mmcblk IIRC. It might give a clue as to what the problem is.
I have several Nokia phones and got used to hot swap memory card function but seems that N900 is like old 9300/9500 which needed to have back cover installed before sd card activates. I formatted my card several time before discovered to cover issue.
