I have one of those spotlights and had the exact same problem. It came on for a brief moment and then wamm, nothing. Plug it in, and it oscilliated back and forth from charging to full, yet not battery charge indicator. I'll bet you a million bucks your fuse inside the light is toast. Since it's inline with the battery the charging circuit most likely can't read the voltage and so gets easily confused. I opened mine right before calling their support line and notices the fuse was popped. Placed another 10 amp auto fuse in there and thought all was well. Popped again later (usually when trying to impress people, bad luck?). Upgraded to a 20 amp. Lasted a bit longer but still went. Finally settled on a 30 amp and all is well. For whatever reason it draws more current during the initial warmup of the bulb but then settles down (I hope, no fires yet!).
If you take the back cover off (two screws I believe, and then it twists off) you'll see the battery. It's a bit snug, but you can get it out, be careful the battery wires are a bit short. Unhook those and peer inside and you should see an inline fuse holder, I had to use some long needle nose pliers to gently tug it out a bit since it was stuffed in there. Change the fuse if it's blown, and tuck it back in. Getting the battery back in was the most challenging since there are some plastic parts of the casing that the battery connectors can't get by. You have to place the wires just right so the battery doesn't pinch them. So far my spot light is working great, even took it on a long walk in the wood and I would say their runtime for 70 minutes looks pretty reasonable so far. I just bought another one for a gift, but haven't changed the fuse out yet. I want to see if mine was just a fluke or what. Hope that's your problem.
On a lighter note, I recently helped my uncle get a 32 in flat screen tv for about a $1. He got it from someone who didn't want to take it in to get it fixed and just bought a new tv. Took it apart and guess what was wrong, blown fuse!!! Great upgrade from his old old tv for the price of a 3A fuse.
Rob