This is what I posted on Yahoo answers in reply to this problem a few months ago
may be that the speaker wires themselves are cut. The 700m's have a
problem with the hinge for the monitor cutting the wires to the
speakers due to their placement. You can check out this link:
That details the problems, along with pictures and a nice guide on how
to fix it. It's easy to check... if you look at the top of the
keyboard, you see the Dell logo, and just to the left of that is a
place for a small flathead screwdriver. Pry that up (carefully, and it
must be done with the screen completely opened so it is 180 degrees).
The wires are tiny black and white, 4 of them, in the right hand hinge.
If they are cut that's your problem.
If you call Dell they will tell you that you have to buy a whole LCD
kit (~$500) because that's the only way you can get the speakers. But
you can usually find them on Ebay (I did) for about $25-30 used. Check
out that link for how to do it.
As far as the power, I would check first that the battery is fully and
properly seated, otherwise wouldn't know what to tell you there.
It happened to my Dell 700m and I was able to fix it