Do another starter. Make sure it is of the right volume for your brew and the right amount of yeast is being pitches. Use www.mrmalty.com
to calculate it. You also add the starter when it is fully going for it so the yeast is ready to much at your brew. Just throwing a packet of year in won't do it as the pitch rate is too litre and the cells are still sleepy. Remember, you have already just pitched yeast, and that didn't work.
Its also worth checking the temperature of your brew and adjusting to make it the right environment for the yeast.
Was this brew from a kit, all grain, partial mash? The only time I had a stuck fermentation was from an old kit, which want airatted enough when I made the wort. Oh, good point, don't airate your wort now, its too late and you will encourage off flavours. Instead, remember to properly airate your next batch before adding the yeast.
Hope that helps.