But there are some caveats here. Dr. Ed Wood, who knows more about starters than just about anyone alive, has said he's never had a starter he couldn't revive. It must help to have medical training. However, other people point out that it's not always clear if the starter your revived is the one you started with. Kinda like Pet Semetary, you can wind up with a starter that's similar to what you had, but not quite the same. And there are a few conditions that make your starter not worth the trouble of trying to revive it. So, let's look at the science experiment you are pretending used to be a sourdough starter and see what we can do with it.
Was there mold on the hooch? Is there mold on the top of the starter? If not, smile and skip to the next paragraph. If there is, go to the silverware drawer and get a handful of spoons. Mold is normally a surface condition, so we'll try to get some good starter from lower levels of your starter jar. Start by scraping off the mold, being very careful not to stir the starter - you'll only stir the mold into the starter. When you think it's all gone, get a clean spoon and scrape a bit more starter off the top. Now go on to the next paragraph....
At this point, you should have a light colored layer of starter exposed, free of hooch and mold. Use a clean teaspoon to transfer some of the starter to a clean bowl. Reseal the jar of starter you are trying to revive and put it back into the refrigerator - sometimes the first attempt at revival doesn't work, and you'll need to go back to that starter.
Your starter should take off in 2 to 3 days. If it is slow, or if it isn't responding, switch to three feedings a day, with each feeding being enough to triple the size of the starter. Do that by discarding 2/3 of the starter and adding 1/2 cup of water and 1 1/2 cups of unbleached unbromated white flour. If the starter doesn't start working well in another 2 days of this process, it's time to pitch this starter and go back to the storage starter in the fridge.
Do you remember back in the Starting A Starter page when I talked about how a starter was like a weed patch that you were cultivating? At this point, one of the weeds has again taken over. And it is a very hard weed to eradicate. I know of two people who were able to beat back the protein-eating bacteria and have their old starter back. However, the other guy and I both found that the next time we skipped a starter feeding the bad bacteria took over again. The starter was undependable and unstable. Pouring it down the drain and starting over was the only real answer.
Once you think your starter is doing well, make some bread with it. If the bread is OK, then your starter is probably OK, so you can pitch the rest of the stored starter and save your recovered starter in the fridge.
An ounce of prevention is worth several pounds of flour.... so I hope you never have to use the ugly forgotten starter recovery notes!