Exposure settings keep changing even though on Manual mode (Nikon D80)?

I have Nikon D80 and I photograph in the manual mode. I set my exposure settings, but nevertheless, each shot that I take has different shutter speed, thus resulting with different exposure on each photo. The camera seems to be playing with light on it's own.

I'm sure there must be something in the settings that could fix it so the camera won't be adjusting itself to light on it's own. Any ideas on how I could fix it?

Are you sure your in full manual? Can't be. You must be in manual in manual aperture and not full manual. In manual aperture yes the camera will set its own shutter. In full manual it can't unless there's something wrong with the camera.

First make sure you're in full manual.

- rotate your mode dial to "M"

- make sure auto ISO is OFF

- be careful to knock the control dial accidentally

- make sure bracketing is turned off (press and hold the BKT button that's placed below the flash button, and rotate the main control dial until the top LCD reads "off" or something like that)

If your camera is still randomly changing exposure settings on its own, then consider calling Nikon's customer support or refer to the trouble-shooting section of your user manual.