Help on N73 Music Edittion?

Hey guys , I got a new problem about my phone.

The problem is everytime I leave my phone alone on the table it turns black screen and when my friends sent an SMS to me , I would only receive it only when i hit any button on my phone and the time received is when i hit the button, any ideas how to enable my phone to receive SMS in that black screen mode?

Another problem is that when I went SMS to radio station in Singapore 's mediacorp 98.7FM
I would end up getting an error saying

Text message:
Check network
servies

Im using a prepaid card and Im not sure if using a prepaid card would affect it.