Thanks for the tip. I cleaned and sanitized an old growler, boiled a qt of water, stirred in 1 cup DME, gently boiled for 10 min, cooled, put in growler, shook for 2 min, added ENTIRE yeast vile (had to beat on it to get it all out), shook for another 2 min, sealed with sanitized airlock and we got bubbles this morning! I can't believe it worked!
That was probably a bit too much DME - you want your starter wort to have a gravity of about 1.030-1.040. I use about 4 oz. (by weight) DME per liter of water (I don't know offhand just how much of a cup 4 oz. of DME is). Even though Palmer recommends the same concentration that you used, 1/2 cup DME to 1 pint of water (3rd edition, page 73) and he says that gives a gravity of 1.040, I think that must be wrong. I remember calculating that once and came out with a gravity of over 1.060. Maybe someone else can weigh in on this. At any rate, your starter should still work OK as is.
Another tip for starters - you don't want to seal them with an airlock - the yeast need oxygen to grow - with a starter, you are trying to make yeast, not beer, so you don't care if the beer ends up oxidized. I use a foam stopper in the mouth of my flask, but many people just cover the top with a piece of sanitized alum. foil crimped lightly over the top to allow air into the container. Shake the starter every time you walk by to keep the yeast in suspension as much as possible. When activity dies down, cold crash overnight and discard the beer, pitch only the yeast slurry (you can pitch the whole thing, but I prefer to pitch only the slurry).