Does anyone out there know if I can reset the main quest in Fallout on the Xbox 360?

The problem: I'm attempting to complete 'Waters of Life' at the moment, but I am unable to advance because Liam Neeson and all of the rest of the scientists won't enter the Jefferson Memorial. Liam keeps telling me to clear the place of Super Mutants. Of course, the Memorial building has been cleared out. (I went to Jefferson Memorial instead of learning about Liam's whereabouts from Three Dog.)

The possible cause: When I started the game, I wandered around and completed side quests before focusing on any of the main quests. After saving the brats from the slavers and then traveling to Little Lamp Light, I (maybe through a glitch) entered Vault 87, came across Fawlkes and retrieved the GECK. Afterward, I found myself at Raven Rock, talking to Eden and then convincing him to destroy himself. This caused me to jump into 'The American Dream' quest. Now, I'm told to go to the Citadel, but I cannot enter the Citadel or advance in this quest either.

So, is there a way to reset the main quest, or has my wandering buggered me out of being able to complete the game properly? I have put a lot of time into the game thus far and I can't be bothered to start over. (I hope this is not the only answer available.)

Thank you for your time and attention.

The only way to reset the quests is to use the command console which is only availiable on the PC.

On the consoles your only option is to load a save from before you entered Little Lamplight and Vault 87. If you don't have a save, you'll have to start over I'm afraid.

Did you get the message that you have cleared the Memorial? Check behind the purifier (inside), one always gets stuck back there for me. You've cleared out the sub-basemant as well? What glitch at Vault 87? Specify..... On 360, as DevenTarn said, the only way is to reload a previous save.... save often with any Bethesda game.

I assume it was a glitch because when I first found the entrance to vault 87 (within the caverns, not the one by the back gate) I received a message saying the door was locked and I needed a key. A day later, I went to the same location and it was open. I hadn't spoken to anyone or retrieved a key from anywhere, so I went right in and (presumably) accidentally did the 'Garden of Eden' quest.

In the Memorial, I have cleared out every area that is accessible to me, but not the water purifier. I can't get in there. The intercoms don't work and there is a man standing with his back to me. I'm thinking that is the Colonel who is supposed to show up after everything to be done in the Memorial has been.

Weird how you could get into 87 then. You're gonna have to reload a save prior to going in there. You need to clear out the purifier and help dad first, help Dr. Li and her little troupe, then talk to the boys at the Citadel, then... you go to Vault 87. Then, after retrieving the GECK you find yourself in Raven Rock.