Near the top of the fill valve you should see a small lever (its attached to the float). if you gently pull up on it does the water stop running into the tank?
I meant to send this to you as an info request. I will assist you further when you respond to me. sorry you had to wait so long for a response from the site.
Okay thanks, XXXXX XXXXX wanted to see if it was stuck a bit. I am suspecting that your valve is defective thus unrepairable. They cost about twenty five bucks at any hardware store. It is a universal fill valve Brand name Fluidmaster 400A.
I see you are trying to get through the weekend though so lets try and see what we can do temporarily. Running vertically down from the end of that lever, do you have a thin metal rod or a plastic rod with what looks like some sort of track (or threads like a screw) on it?
here is a link to guide you the rest of the way.
looking at the fill valve kit (#1) and part #83451. you will access this by removing the dome shaped cap at the very top with a flat blade screw driver. don't worry about braeking it, it is purely decorative and is simply a non functioning cover.
Next, looking closely at the top you should be able to see that by turning the small lever gently the portion that it is attached to will rotate slightly (over some small clips) under neath the cover just removed. This will remove the lever and part #83143 will be able to be cleaned with a clothe and warm water.
Next place a small cup over this area and turn the water fill valve open a bit to flush out and debris.
Put back together and hopefully tis will work properly again.
If not the only thing you can do is replace the fill valve. In the meantime, you will need to shut your water valve on and off to stop the running water until you can replace it.