sometimes it is simply debris in the camera body stopping the shutter from functioning properly. Lens off, air can in, see if anything is coming out of there. After that, I would with lens off look into the camera and do some eyeballing on the equipment for anything not aligned or where it is supposed to be. Try a few settings on bulb, seecond, half second. and work up the shutter to see if everything is still responding as it should.
Could be something simple like dirt, could be the controls of the shutter in the camera. Hope for the dirt, otherwise your looking at some basic repairs that are going to have to be done to the camera through your local repair shop.
Best of luck