truck won't start or turn over on 2001 GMC Sierra 2500 HD

My truck will not start. I went out this morning and stuck my key in and it didn't do anything. I looked down and the gauges were dancing all over the place and I could hear the battery drawing juice, even without the key in the ignition. Does this mean that the computer board is going? Do I need a new ignition? I did disconnect the battery so it would quit drawing juice that I could hear thou. Please help!!

Asked by for the 2001 GMC Sierra 2500 HD