This evening out of the blue, my faucet stopped working. It's a two handle system. The spray gun works fine. I checked the aerator and it was clean. We just installed a PUR water filter on the end about a month ago but I doubt this has anything to do with this. Also, there is a very small (dripping) amount coming from where the spray gun attaches to underneath the faucet. What's the best thing for tightening these things because they are harder than heck to get to.

Check the water filter first it could be your problem. As far as the sprayer fitting the only way to tighten it without having the sink out is to use a pair of pliers if Ive missed anything post back and we will try to help. GOOD LUCK, AC

I took off the water purifier thinking it may be the aerator but no such luck. I have also taken the cap (nut) off the top of the faucet and actually removed the faucet. Even now when I turn the water on hoping it will shoot out and make a mess it is not.

Its going to be the diverter in the faucet itself you will need to remove the nut on top of the spout and if you look inside you will see two notches on a plastic piece that is the diverter the best way to take it out is with two flathead screwdrivers

Took the faucet out to a plumbing expert and he had never seen the valve or diverter that was in this thing. I've taken numerous things to him and he always knows the answer. In any event, bought a new Delta faucet and the wife is happy again. Thanks!