nokia messaging problem
 

hi am new to this but i recently purchased a nokia n900 and after few weeks , now the sms that i get does show up properly , once i restart my phone i get to see all the messages that i couldnt see but again after sending a few msges again the same problem arises, i can't see the messages i sent and when i try to sent a messgae it shows" delivery message failed for -" and this keep on happening

plzz help me :(