My Minecraft world won't load and I can't edit the world to make a copy.

Me and probably seven or eight of my friends were playing on my Minecraft world and one day. One of my friends decided to go -7,000 blocks off the map and every time he would join he would lag out the world. Then me and one of my other friends tried to get him but it lagged the world so we gave up trying to get him. Five minutes later the world crashed and wouldn't load. I can't load in the world or edit it. I tried to use my saved data but it wouldn't work. I even looked up how to fix it and nothing worked. I even deleted most of my worlds. When I ever click on the world it says " There was a problem loading this world". I had a year worth of progress on there and I really don't want to lose it.