Unable to use Optic drive

Hello, I wrote about this a couple of weeks ago. I've narrowed down the problen.
Ive got a Macbook 13" 4 yrs old, 120 gb, 2 gbram, intel core 2 duSX Mointain Lion.
The optical drive does not work. Usually on putting in a disc its spins it around for a while but then stops and refuses to eject the disc.
I definately rulled out the discs, all work o.k. elsewhere. So I bought a DVD writer, external, plugged it in using correct usb cables, same thing. Lights come on showing it is searching but then stops.
I rrealised that if I tried to eject the disc whilst the disc was spinning inside, then it would come out. So I thought, is there something wrong with the power and it runs out after about 30 seconds.
So, to definately settle the matter, I bought a new battery (and I keep it plugged in to the mains) but, no different, neither the original optical drive nor the brand new dvd writer work. The dvd driver works perfectly on other computers.
So, it must be SOMETHING in the macbook, either software or, I don't know.
Anybody got any ideas Mike

Is the external optical drive mains powered? If not you may need a hub and a dual USB connector if the MB has enough power from a single USB port.

Picture to illustrate what harryb is talking about, and I think he has hit the nail on the head (Mac USB ports are in some cases a little underpowered compared to PC USB ports, particularly on an old machine like that):

optical drive problems

First, thanks very much for the help. Yes, I think you are both correct but it still hasent solved the problem. Ive tried with a dual usb cable as you displayed and, yes, it did do the trick on another laptop I borrowed to try and get to the bottom of the problem.
But, not on mine.
I think you are thinking along the same lines as me, there is a problem with the power somewhere. The thing I am afraid of. One person I spoke to, good on computers but doesent know a thing about Macs, he told me so, says it may be on some board inside the laptop, I didnt catch what sort of a board but he did say that the cost of putting it right meant goodnight to my Mac which is 4 yrs old!!!
You cheered me up a bit by saying that Macs do have a bit of a problem with usb ports. At least I might not be alone.
Of course, any further advice as to where I should go from here would be much appreciated Mike

Oh, and to Harry. No, the optical drive is NOT mains powered. Do you think I should buy one? Mike

Think resolving what it is may be better. Can you borrow a mains powered unit at all?

Yes, I am on a promise to borrow one on next Monday 2 c what result that brings. I will write with the result. Heres keeping my fingers crossed HaHa Mike