Hi. Ive got my NCR Rangers uniform after meeting Cato at his hideout and am heading to Hoover Dam to kill the president only everytime I arrive I get shot at and the mission fails.Is Cato at hoover dam, if so how do I report to him without getting shot? Im assuming I have to report to him before killing the president.

i would say use this as a guide
http://fallout.wikia.com/wiki/Arizona_Killer
i have never done this mission but one thing in the wiki stands out to me, "When you're going to the Dam, be sure none of the Rangers see you, otherwise they will see right through your disguise and start shooting at you."

it's easy just keep a little distance from the rangers talk to him and the president will arrive

Don the disguse and use a stealth boy to sneak, stay away from rangers and dogs and you should be fine.
You can sneak around to kill Kimball, shoot him, or do both get bored and frag him with a missile launcer half way through.
Guess what I did, go on guess.

Thanks. Problem is they shoot even when Im at distance and then it says mission failed. Will try again.

Did you try sneaking from that distance, ( sorry I don't mean to imply anything with that question ).
As if you have on the disguse and are not spotted they should remain yellow.
Also did you speak to Cato first and follow him to the dam, after the rest he makes you take.
He should be at first along the Colorado.

I spoke to Cato but I made my own way to the dam. Im gonna go back to my auto load and start the mission again. I ve spent a whole day on this. Thanks for the advice......Still no luck, Ive watched walkthroughs and people dont get shot, everytime I approach Cato at the Dam I do. Ive tried sneaking and walking in the Trooper armour. Must be a glitch.

The thread's title gave me a pause. For a moment there I thought it was about something else entirely...

Did you have CL armour or Khan outfits, or powder ganger gear on prior to heading there.

If so put the same type back on and take it off again as this may be the glitch ( it normally is with instantly hostile foes ).
If not sorry that's all the info I know, so I hope it works for you, and good luck.

I filled the "safe room" with mines then blew up his Vertibird in the middle of the speech so he and his Rangers would go there to hide.