Im at the end working with the NCR and the president gives his speech then gets his head blown off by sniper, I cant find where the sniper shoots from is there anyway of stopping the president dying?

Yeah he's on the tower behind the president when he's speaking. After you speak to Ranger Grant (tell him everything is set), quickly run and climb up (using the ladder) the tower behind the podium (you should see a NCR Ranger up there initially), shortly after the president arrives and starts walking to the podium (around when Hail to the Chief starts playing) another NCR Ranger will appear out of a hatch on the floor of the roof. Kill the NCR Ranger that appears (he's the assassin), after killing the fake Ranger use the radio on the table to tell Grant about the sniper, then quickly climb back down from the tower and run to the speaking area where an engineer with a knife will make a run for the stage, kill him and then the president will leave and the mission will complete.

Another option is to go up the ladder after speaking to Grant, and check the vertibird. If you pass the skill check, you find a bomb. You can then go back immediately to Grant, and they call off the whole thing, which also saves the presidents life.

Ok cool thanks guys, I didnt pass the skill check when I searched the vertibird so looks like im going with the first option. Thanks for your help, When this is over I gotta complete it the 3 other ways.

Or pickpocket the engineer on the roof, and then tell Grant what you found. (if you cant pass the skill check for the vertibird)

Just a warning, this quest is horribly buggy. If you seem to have issues initiating the next part of the quest look for help on the internet.

Ok thanks, They only thing I have noticed is its extremely laggy when you visit hover dam, Its almost impossible to play but luckily its the last mission you have to do so I can just about tolerate it.