I had this problem, in my case the shutter was completely open thus not stuck closed neither stuck open.
I removed cleaned and reconnected the two CMOS sensor ribbons (I guess one is the power and one data ?). There are two white lines on the PCB in a way that when the cable is correctly plugged in you only see one...
After that the camera started to work normally.
I can not be sure but my opinion is the cable got loose by impact\moving ecc. I used some tape to fix it a bit more.
I hope it helps...