Fran, seeing as how you planted them when they were supposed to be in full flower I think it comes down to your accepting that this season is a lost one....and you should look forward to planting them next spring about the time you put out your annuals.....maybe a little sooner..when the soil has warmed up sufficiently.

As it is, you may as well leave them in the ground until after a hard frost....which will turn the foliage black.
Then you dig them up and store them in a cool, dry, dark environment. Bury them in peat moss or dry sand.
Let them dry though for a day or so in your garage so as to not store them in a too moisturized condition.
Moisture around the soft tissue of your dahlia tuber can initiate mildew or rot. Let them dry out a bit before you store.