Last summer I spent a whole weekend convinced my riding mower's engine was shot. I had the carburetor half apart on the garage floor... turned out the fuel shutoff valve under the tank was just turned off. My own dumb mistake cost me two days of swearing at a perfectly good machine.
Why is it always the cheapest, easiest part that causes the biggest headache? It's like spending an hour trying to fix the clock on the microwave before you realize it's unplugged.