SO I beat Dead Money and I wanted to try and play it again but I was already aware that I couldn't go back to the Sierra Madre so I decided to play a new game with a fresh character and leveled her up to 20 and I am here facing the entrance to the Abandoned BoS Bunker and it appears that I can't enter it because I have to use a key which didn't happen before which is rather odd. can you help me here I tried deleting the dlc and re install it but I still can't enter.

I am haveing the same thing and it svcks. I have dumped it and reloaded it with no luck. I would like to finish the game with the dead money gold but I have a save out side the bunker.

Of course you installed the latest patch...

Yes I did and now I can not get in or out

Well, I know that there's a workaround to fix the "key needed" message you could have when you exit the bunker after completing the DLC. You should delete the system cache of your Xbox (deleting the patches), load the game (select no when the system ask if you whant to update), load your save, exit the bunker. Then install the patches.
Since the abandoned BoS bunker was made inaccessible with the first patch, perhaps if you delete the patches, enter the bunker, save your game (do NOT overwrite the previous save), then install the patches...
But beware: uninstalling the patches may cause some problems to your saved game, overruling some of the patches benefits.