Shutter speed - main dial - manual mode not working - 5D Mark lV

[JT7]

I am unable to change the shutter speed using the main dial while in manual mode.  I was shooting in the dark last night and wonder if I inadvertently pressed a button that could have locked my shutter speed.  The Lock is in the Off position. The Quick Control dial will adjust the aperture.  I can use the Quick Control button and the screen to adjust the shutter speed while in manual mode but would like to use the main dial as before.  Any suggestions?

[rs-eos]

When in doubt if you inadvertently changed something, reset the settings to its defaults.   Hope that will resolve the issue.

[ebiggs1]

Besides the full reset, try a different lens, a new battery and CF card which is about all you can do. Plus a call to Canon 1 (800) 652-2666