My toilet shut off valve won't spin back onto place and I notice a white tube is now exposed. I tried to shut off the water and the white tube is now popped out and the silver knob I use to turn water on and off just keeps spinning. The water filled into the toilet tank, but I cannot get the white tube back onto place, nor can I get the silver knob to push it back into place. What should I do?

Really guessing about what you are saying but I think you are saying that the handle on the shut off valve under the toilet turns but won't shut off the water and the supply tube between the shut off valve and the toilet has come loose.

Can you post a picture?

There is a screw in the middle of the handle that screws into the white stem. Make sure it is tight. If not, take a screw driver and tighten it. If that doesn't help than remove handle and use small channel locks to spin plastic stem in clock-wise motion. That should turn off water to your toilet. Milo