While trying to shooting at 2500 ISO in a dark music jam, when I push the shutter it just stays open, the plus/minus exposure dial through the lens flips to far left, and I have to change the setting to make the shutter finish.. then no shot... do I have wrong settings somewhere that is causing this.? I have a 35mm 1:1.4 lens attached...Canon
Well, without knowing anything about your Canon settings beyond ISO, there could be several culprits:
1) You have a Canon SLR and have turned on "Mirror lockup" so depressing the shutter once flips up the mirror, turning the viewfinder black. If you press the shutter release a second time, the camera will take the photo and then flip the mirror back down again. Here's the Canon KB entry on 5D Mk II mirror lockup -- so many different behaviors.
2) You are in Full Auto or Aperture Priority mode and ISO 2500 isn't nearly high enough (easily possible in a dark studio). The camera is selecting a long exposure time and you are cutting it off by changing modes before it is done.
3) (Less likely given your description): You have set the shutter speed set to "B" for "Bulb" exposure. The shutter stays open as long as you hold down the shutter release.
2500 ISO is not actually very high. Indoor lighting is much dimmer than people usually assume (human vision is remarkably adaptive). In a "dark music jam", it is very likely that even if you have your aperture wide open at f/1.4, a long shutter speed is required.
In other words, everything seems working as designed and expected.