Wasn't sure where this belonged, topic wise.

While the quest was active to go to Lamplight and try to find a way into Vault 87 ("Picking up the Trail" I believe is the name of the quest?) I made a few stops. Specifically, I stopped in Paradise Falls and rescued the slaves (oh look, there's a bunch of kids there too) and then I went to The Pitt and did that whole quest line. This is my first time through, fyi, so I didn't think twice about side-lining myself.

About 1/2 way through in The Pitt I randomly get the "Picking up the Trail" achievement and notification that I successfully completed the quest and my quest log updated to "find the G.E.C.K." "Alright", I figured, "I'll cross that bridge when I get there". Well, I'm there.

Now when I go to Little Lamplight I'm not getting any of the dialogues to access the methods into Vault 87. Joseph won't talk to me about the computer, and the Mayor won't talk to me about Vault 87. I've spent about 40 minutes running around talking to the various people over and over and over, no luck. People who will give me directions are willing to tell me that I need to head down the tunnel to Murder Pass, that it's dangerous but I can look at it from North of the Souvenir Shop...but no one will talk to me about actually passing through the gate.

My character has 8 Charisma and 8 Intelligence, he's level 27.
His speech and science are both at 100 and he has the Child at Heart perk.

I have no idea what to do next. I even tried to find a way in from the surface with heavy anti rad drugs and resistant drugs / clothing.

Any suggestions? If there's something I can do that doesn't involve me going into the console that would be my preference but any suggestions at all are appreciated. My game is obviously against a wall at the moment.

Thanks

I think you have to do the water of life quest, i think that is what it is called.you have talk to the guy at the citidale, and he tells you their may be a back way thru lamplight cavern.

yes that quest can be a little buggy at times . And i have no help for you because you said you didn't want to use the console . i was just going to suggest you reset the dialogs it will allow you to cycle through all dialog options again . But there is a down side though you cant just reset little lamplights dialog it resets all npc. Its not that big of deal really. that would be the safest way because trying to sneak in without doing it the right way can bug your game even more. I had the same thing happen in my game . And i just used th console code to turn off collision and walked Thur the back gate . But even that was enough to really mess my game up for some reason. And if you don't want to use the console because of achievement. just after you reset the dialog save and exit out of game then restart the game and you will still get achievements.
EDIT and even if you did manage to get to the front door without dying from radiation you cant get in that way ,at all.

Yeah I found that out the hard way on my first ever playthrough, finally got to the door after taking obscene amounts of radaway and the damn thing is locked, upsetting.

I don't own FO3 for the PC but I used Oblivion on the comp, is the computer you need to hack locked until you talk to the kid? If so can you use the console to unlock it to be hacked sorta thing?
Sorry I don't know much about FO3's console at all and can barely remember the quest, the back door is unpickable locked but can the console open it? Beats using collision...