Motorola SLVR L7

I am unable to send or receive multimedia text messages. Every time someone send me a picture through a text message it doesn't show the picture it just shows alot of ? marks. When I try to send them it tells me unable to send message. I tried to set up browser settings for Cingular Media Net, from a posted website off of this forum, but that doesn't work neither. Someone help me plz 😢