Whats going on with my van?

I got a 2000 Plymouth Grand Voyager 3.3L 148K mi. I have a few electrical probs. This morning I went to start it and It was completely dead, no electrical power whatsoever on the van. i take my key out of the ignition and im hearing a weird humming, crackling sound that only stops when my foot gets on the brake. i turn the key back and forth from lock to start; NOTHING. Batt terminals are clean and tight. two min pass and my dome light comes on. WTF? i try key again and the electricity disappers again. arrrrrrghh. after 4 episodes of this, it starts with no issue and hasnt acted up since. I gotta figure it out cuz i run a daycare and this incident left me and my five six year olds and two 9 months old stranded at the local mall for an hour. any suggestions?