What to do with the dispatch number?

I have a D510 laptop and since the past few months i am experiencing some problem with my sound. After 2 to 3 hours of system time there is no sound from the system.

 I chatted with Dell support through the chat link. I described my sound problem and the tech said my motherboard needs replacing. After supplying the requested info, I got a "dispatch number". The tech also said "We have created the dispatch for you and you will be receiving it soon."

What is a "dispatch number"? And when I receive "it", would that be a new motherboard? Also, I just sent the e-mail today, how long would it take before I receive it?