The answer to 'toilet won't flush' is that there are several common causes, including a clogged toilet, a problem with the flush mechanism, or low water level in the tank. Symptoms may include the toilet not flushing properly, water not draining, or water not refilling the tank.
For minor clogs, you can try plunging the toilet or using a toilet auger (plumber's snake) to clear the blockage. If the issue is with the flush mechanism, such as a faulty flapper or fill valve, those are usually inexpensive and straightforward DIY repairs. However, if the problem persists or you're unsure of the cause, it's best to call a professional plumber to diagnose and fix the issue properly.