No sound from built in speakers

Hello
Like in title i don't have sound from built in speakers in macbook
headphones or external speaker working ok.
I have noticed that when nothing is connected to line out then there is red light from line out connector.
I know that built in speaker are ok because when i turn on my macbook there is sound but after system boot built in speaker don't work.
I have macbook MB403PL/A.

i know it sounds stupid but , have you tried the vol + vol - on yout keyboard?

If its not the volume button thing, then it sounds like the same thing that happened to me, only I could hear out of head phones when they were plugged in. If its what I think it is then the micro switch in the line in, input that has gotten stuck. You could try a quick fix by CAREFULLY putting a cocktail stick in there and unjamming it. However its dodgy as doing that and its not guaranteed to fix the prob. So I would suggest taking it the Apple shop and they'll sort the problem out.
Hope this has helped!