Is it in a pot? I didn't see anything in the original post that said that.
Ms b, let us know whether it is in a container or in the ground.
You said neglected and not fertilized. Perhaps it needs less neglect and some fertilizer? (But nothing too high in nitrogen, some bloom booster type phosphate fertilizer in early spring.) Do you prune it? Pruning helps the plant focus on flowering, not just growing more and more vine:
Like another vigorous vine, the grape, the wisteria will produce excess growth with limited flower (and fruit) production unless the vines are pruned. Many gardeners prune grapes and wisteria in mid-summer (and perhaps again in the fall as you described) to remove much of the excess vine production. Then, in the early spring both of these vines may be cut back so that only 3-5 buds remain from the previous year's growth
Sometimes root pruning can shock it into blooming. In the spring, push your shovel into the ground to cut the roots, all around the vine, but 2-3 feet out away from it. (This is presuming it is in the ground, not in a pot.)
I don't quite understand how "neglected, not fertilized" fits with "tried everything I can think of," but tell us more what you have tried already.