ok here is the suggestion bcz i used to lost mine too

if u've lost it right away without making any changes to the keyboard settings, here is the way

make sure u didnt slide the hard keyboard out

then turn the device off for about 5 minutes .... do not touch anything ....after that, turn ur n900 on .... now! try it

i've lost it several of times and this way always works

however, after fixing by this way, i never get this problem again