Been there, done that!
I assume that you're fermenting in a glass carboy. That is sometimes a
problem because of oxygen deprivation in the fermentation. The yeast needs
at least some access to air to propagate. Also, it has to have the correct
nutrients available, and prefers to have some solids in the juice.
Stuck fermentations are sometimes very hard to restart. At 1.030 sp. gr.,
you're at about 8% residual sugar. That's not as bad as it could be. (If
you're stuck at 1.5%, you have a really bad problem!)
I'd recommend going to the store and buying a couple of bunches of fresh
grapes, squeezing them for the juice, and making a fresh starter. Also,
rack the stuck wine with splashing into another container, and add some
diammonium phosphate (About 10 grams should do.). Be sure to re-hydrate the
yeast before using it by mixing it in warm water (100 deg. F) for a few
minutes. Don't let it sit around after rehydrating! Add it (the yeast) to
the fresh juice, which should be at room temperature, within 5 minutes.
Once the starter is going vigorously, mix some of the stuck wine into it.
Not too much at first; the idea is to get the newly active yeast "used to"
the presence of *** gently. Let the activity build back up, and add
some more stuck wine. Incidentally, you don't say what strain of yeast
you're using, but some of them are very sensitive to *** and low
temperatures. I assume that you want the wine to go dry, so use a vigorous
strain like Montrachet or Chanson. I don't recommend heating the
fermentation of a white wine, but keep it at or about 20 C.
If you can get actual yeast nutrient, that's even better than diammonium