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
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.
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.