I have tried all i can and even lowered my difficulty but for some reason i do no damage to Alduin.

Any help?

Do a reload?

How much damage are your weapons doing right now?

Edit: Have you tried using Dragonrend on him? He only takes damage when he is on the ground.

Was it really that simple? Gee don't i feel like an Idiot, thanks

Defeated him! You don't know how happy that makes me to know that i can do the Main quest and my No Glitching/Fast Traveling Character isn't ruined

So was it using Dragonrend the reason he wouldn't take damage?

I don't know, i was using it before i reloaded and he wasn't taking Damage.

There is sometimes a bug that makes him invulnerable. I had it, but worked through it. While I'm not certain, I seem to remember it maybe having something to do with attacking Alduin while he was still talking to Parth or something.