I cannot get back into the strip it says that I require a key even though ive already been in there why am i suddenly locked out and how can i fix this AHHHHHHHHHHHHHHHHHHHHHH

this happened to me as well, I did not even flinch, I just opened console, typed unlock, and boom back to hokers and gambling

Or take the NCR monorail.

I cannot go on the monorail because i get shot at by ncr secruity guards then every person in the ncr starts shooting at me... Oh and im playing on the xbox 360

Find yourself some NCR armor and then get on to the monorail.

Easiest place if find a dead soldier. There are 4 in a house in Nipton.