fallout-4
When I'm in Nuka World, I can't actually see the map. It's just maybe one or more icons crammed into one corner of the normal Commonwealth map.
That's what it looks like:
I do have mods but none of them add new areas, mess with the current ones, and I've never had this problem before.
I entered Nuka World last night. The Nuka-World Transit Center is way to the west edge of the map.
I fast traveled to the Lonely Chapel to its northeast, and just walked right up to it. There's a highway that leads into the main entrance.
I didn't want to enter the main entrance, since there were enemies there and I was using a stealth character, but I found a gap in the fence to the north of the main entrance.
Here's a video on YouTube of someone approaching the transit center from the Sunshine Tidings Co-Op. The transit center comes into view around 4:40.
You restore power at the end of the Power Play quest, which is the next quest after you set up the Raider outpost during the Home Sweet Home quest in the Commonwealth.
As Serverfrog said, you need to build the Raider-gang specific flagpole in the settlement to claim it after you have either killed the settlers or told them to leave. When you talk to Shank, you decide which gang you want to man the settlement you chose to take over. You then have to craft the flag that corresponds to the gang you selected.
In the crafting menu, all the way on the right is a "Raider" section. Within that section are the flags you need to craft and place. I believe it's 2 steel and 2 cloth per flag.
Best Answer
Answer was in comments.
As The Mattbatt999 suggested, it was a mod that was causing this issue. Disabling the mods on the game resolved the problem.