Before I started my Yanmar 2GM this weekend I unpluged the shore power and had the battery switch on both. I turned the key over and the light turned on as usual and the buzzer came on as usual. When I went to hit the start button nothing happen. I plugged in the shore power and it started right up. When we went out sailing we motored out for 20 minutes and sailed for 2 hours. During this time the insturments and radios were on. When I went to start it after the 2 hours it started right up. Any ideas on how to diagnosis this problem would be greatly appreciated.