So let me try to tell you what is going on. A few days ago, everything is working normal with my toilet. When I go to flush it, it flushes fine, and the water fills up slowly, but not all the way. There is a sucking type noise as the water is only filled up partly and does not cover the entire whole on the bottom. It finally fills up about half full. I test it and flush the toilet, and it works fine, but again the water only fills up about halfway.

I proceed to try to manually push down on the "float cup" type ballcock so that the water fills up the toilet a little more. This is when all my problems start.

Now when I go to flush the toilet, it starts to flush and halfway through, instead of going down the drain, it continues to fill with water. At the same time, the toilet tank fills up until the ballcock hits it's level and automatically shuts off.

Not sure what is causing this overflow. Is the level of my ballcock set incorrectly? I've tried looking at troubleshooting guides online without any luck. Any help would be greatly appreciated.