Question abnout why my windows live mail will not work?

i had someone from at and t and microsoft suppsoedly say now it shoule work and it still does not work. I am new to computers, and i am trying to buy and sell on craigslist ect, but when i click on the address to respond and it goes to the windlos live mail it lets me type in the message but then this error comes on the screen and it can not be sent, i am so frustrated after six months of trying everything abou ready to just give up. Now i have to write down the address and type it in and then send it with the yahoo mail. I know stupid but not sure how to copy and paste it inot the address area yet either. No rude comments please just kinly hlep me. thank you here is the error code. 0x80070057