Having a bit of trouble, I started the 'Last Voyage of the USS Constitution' mission, and ever since my game has been incredibly glitched. I checked the walk through, and it told me that the mission takes me to the Corvega Assembley Plant, but my marker took me to Fort Hagan, and when I got inside and cleared it, the marker is behind a chained door. So I followed the guide and went to the Corvega plant and went to the box that the item is supposed to be in, and it was just guns and ammo. So now, I can't complete the mission, and also my game keeps throwing my weapons out of my hand, and randomly re-loading one of my quick saves as I walk along. Please help me! I'm so frustrated. I tried reloading and shutting the console down and everything, and I don't know what else to do. Even when I don't do that particular mission it still does these things.

FYI, I found my way around the chained doors at Fort Hagan and then exited via the chained door.

I can't get the Captain to start the final leg of the quest, but I did get past where you are.