Stuck shutter on Lomo 135m

Today, my grandma gave me her Lomo 135m camera. It was almost not used at all, as she found the controlls to be too complicated. When examining it earlier today shutter seemed to work fine, but now it is not oppening. I have tried unjamming it with a tiny screwdriver and that gives me one shutter release when winding the knob. Also one thing that worked earlier is the flash unit, which still works now, just not when shooting the camera. When pressing the trigger the mechanism does work and film does advance, its just the shutter not opening regardless of the shutter speed i select. Any possible causes and/or solutions?

Hello Filip and welcome to the forum. I can't help, but I'm sure there are members who can help, though you may have to wait a while for someone who can help to reply.