Hi, thank all of you for your help!
I found the reason why I cannot activate the on screen keyboard. I installed MSCIM for my mother tongue input, and it 'take over the input interface from the default hildon input method.' The link below clarifies it, #21.
http://talk.maemo.org/showthread.php...453#post522453

However, your methods are useful as well. I will try them when necessary.