I'm just wondering why I opened the game and was immediately attacked by (at least) every NCR functionary in sight and my reputation with the NCR went from liked when I last shut down the game to neutral now. I have specifically played the game (this time) to stay on the good side of the NCR and so I haven't killed any NCR affiliated people or stolen anything from them nor beeen caught stealing from anyone else. I recently completed the HELIOS One quest and turned the power on for all but when I left HELIOS One the NCR soldiers didn't attack and I haven't done any quests or anything else to help any NCR enemies. I think there is a corrupted data file but I have no idea which one. Can anyone help?

P.S. If this is some kind of game glitch I'd like to see it fixed. I am getting tired of all the other technical problems I'm constantly encountering since the day I bought the original Fallout 3 (hard locks, unexpected shutdowns, BSODs, etc. Heck, I just got dropped out of the game, which is why this note is being sent)... through 2 computers and 3 OS'es so I'm reasonably sure the game itself is just weak.

I think the console can make them friendly again.

make sure ur not wearing any clothes of people the nor hates, you know faction armors, like, make sure ur not wearing a legion outfit, or anything like that... cuz i made a similar mistake.

Did you activate the Archimedes security system? That kills all the NCR troops down there guarding the solar panels.
That might be why.

Thanks for the ideas so far. To be clear, I was wearing leather armor and a Ranger hat, and I only started the power, not the weapon. This situation arose after I had finished HELIOS One and the REPCONN quests and returned to Nipton, acquired the info there and sold off my loot to the vendor in Nipton and a passing caravan. I then slept, equipped and walked outside to get the save, checked my stats and logged off the game. When I logged back on I encountered an NCR ranger who started shooting at me. I looked at my Relations in pip boy and saw that my NCR standing had fallen from Liked to Neutral and, of course the NCR was shooting at me..., I dunno, maybe they thought I was asleep on watch or something?

I think the ini or dat file got corrupted somehow.

Thanks again for the advice.

i have had the same thing happen. i play on 360 so i'm not sure that any of the file got corrupted. i also noticed that if i am in good standing with the ncr and i equip their armor my rep changes to disliked (or one below the equivalent).

wow that svcks its probably a glitch or a bug perhaps.

Did you take off the Ranger hat to see if there was any difference?

There are no faction changes by wearing a hat.

Your reputation for NCR has dropped from liked to neutral which sounds just like a faction armour related bug. If it were accidentally killing anyone/stealing or doing a quest with negative ncr faction your reputation would be sneering punk or mixed. I would perhaps toggle invincibility and get out of their firing range while you sort this out. I suggest equipping ncr faction armour, seeing what that does to your ncr rep and then unequip to see if that makes a difference. You could also try waiting three days somewhere where there are no npc's to see if it fixes the hostility.
Autosaves are probably not the best thing to rely on either.