Mark III 5D

[KamdynFuller]

My shutter will not open when I try to look through my Viewfinder. Please help! I can take pictures through the screen but when I switch back to the view finder, it is black.

[KamdynFuller]

Yes, the Shutter is closed.

[Tronhard]

When you open the camera, is the shutter exposed immediately?  If so, then your mirror is stuck in the up position.

[KamdynFuller]

It seems like the Shutter is getting jammed. I can touch it and it will come back down, but as soon as it takes a picture and goes back up it jams again.

[Tronhard]

That would be normal if the camera is stuck in back in live view mode.  If you have not done so, I would definitely do a camera settings reset.   Can you confirm that the mirror, normally in front of the shutter, is always in the up position?  Don't try to force it back down!!!!

[KamdynFuller]

I have already reset the camera settings. I did not force it back down if I barely touch it, it comes down on its own and I can finally see out of the viewfinder. Once I click the button and take a picture, it takes the picture but the shutter is closed and I am no longer able to see out of the viewfinder.

[jrhoffman75]

Looks like you need a mirror box repair. 

[Tronhard]

A good point.  I took the comment to mean about switching back to viewfinder to mean that they had actually knowingly activated the switch.

KAMDYN: please check the diagram on P20 of your manual, shown below: it identifies a button, just to the right of the viewfinder labelled Live View Shooting Switch.  That switches between live view using the LCD at the back, and the optical viewfinder.  Try checking that is not rotated, and if so rotate it back to vertical.
  It identifies a button