My 5D Markiii just failed on me

We're at a fireworks/early 4th of July event and my 5D3 just gave up on me . I think it's a shutter failure, but what do you guys think?
Problem: last week I shot an event and it suddenly wouldn't shoot at the shutter speed it was set (set at 1/2000, but it felt more like 1/15) turned it off and on and it worked fine from then on. Today I had the same problem, wouldn't shoot at the set shutter speed and no burst at all. Powered it off then on and was good to go again, then it just died. I tried a different battery, but have not been able to get it to power back on. Does that sound like a shutter problem or more of an electrical problem? A trip to Canon is in its future, just have never encountered this particular problem before.

Don't think that a bad shutter would keep it from powering on. You can tell if the shutter is bad though. Take off the lens and carefully lift the mirror up with a toothpick(don't force it) and look at the shutter for loose shutter blades.

Thanks, I did that and it looked fine. I tried yet another battery this morning and it powered on and worked just fine again. Very weird..

Maybe it was just a bad battery. Good luck.