The answer to 'shut-off valve won't flush' is that the shut-off valve may be stuck or broken, preventing water from flowing properly into the toilet. This can be caused by mineral buildup, corrosion, or mechanical issues with the valve itself.
Some common symptoms include the toilet not filling up with water when flushed, water dripping from the valve, or the handle being difficult to turn. To troubleshoot, try gently turning the valve handle back and forth to see if it's stuck. If that doesn't work, you may need to replace the shut-off valve, which is typically a DIY-friendly repair. However, if the issue persists or you're uncomfortable working on plumbing, it's best to call a professional plumber to diagnose and fix the problem.