EOS20D won't turn off, take pictures, or show pictures left

Very odd- This just happened after I swiched to a wide angle lens and took a picture successfully. When I tried to take another one, it beeped when it focused, but took no picture. When I looked for remaining pictures, the box was empty. I tried restarting the camera by switching it off- the camera stayed ON in the OFF position!! And if that's not enough, every time i've turned it on since, the orange light stays on and all of the previous symptoms remain. I cannot view pictures I have already taken; I've switched and completely removed lenses, cards; removed and replaced the battery (charged). symptoms remain.
Neither the camera, nor any of its components, have been near moisture, extreme heat, or dropped.
What should I do?