Fallout 3 problem with quest Picking Up The Trail. Help?

When i enter the citadel and i walk up to the guy standing there and it locks me in place and i cant do anything. When i talk to the guy he just says "hail". If i turn collision off and fly over it and i talk to dr. lee, she just says, i need to collect myself, or something like that and i don't know what to do. Help.