Need to gain my rep with NCR, anyone know how?

Do quests for them; kill raiders (powder gangers, fiends, legionaries). Stuff like that.

I alrdy tried tho! I dont get any rep for killing Powders OR Legion!

Then do quests.

I happened upon Boulder City.

I opted to negotiate the release of hostages with the Khans. By time I was done, I received +rep with both the Khans and the NCR

Then I ran into Camp Golf, an NCR outpost. You can gain more rep by doing a small quest in the camp where you help a squad become more like a team instead of misfits.

Yup. That's all I did and I just had something cool happen out of the blue because they "love me so". It was a nice surprise. (Don't spoil it if you know what I mean.)

Helios one, do what the idiot asks you and you get enough fame and a radio to call backup.