Samsung duos sim card error urgent help required

Hello,



I have a samsung duos. whenever I dial a number it shows 'not registered on network'. I havent got any calls or messages the entire day and so I am presuming that people are not able to reach me. My phoe shows sim card error and I have taken out the sim card and inserted it several times. I have also switched on and off my phone several times.

It will be really great if someone could offer a solution.