I know what's going on man... that crap happened to me all the time (wiping after pulling the bottom floor....)

Just try different pull strats and find the one that works for you...
when I pull, like to pull the first hallway all by itself. why? because it's quick and it possibly can save you from wiping when pulling the rest of the bottom courtyard
if you get low on mana, run up above the waterfal and wait for the mobs to gather there, then jump down and use evocation or a mana gem or something.... it works wonders for me
I also like to bring a random healer-class as my fifth because if you have him/her spam heals on you, it can really help (just make sure you cause enough threat to them )

and one question, when you are pulling the mobs, do you remember to blink after you get 10+ mobs? this helps a lot because it will make your ice barrier last longer allowing for bigger pulls.
when i first started doing AoE with my mage, i ran into tons of problems where I would die because i was a little slow on my blink after ice block or something... lol
I like the flamestrike-CoC combo because it causes insane damage and you can use ice elemental to re-frostnova if you don't kill them all

if you are a clicker, it's going to be hell trying to AoE because you will be extremely slow with everything
and when re-speccing, go for something like thishttp://www.worldofwarcraft.com/info/classes/mage/talents.html?tal=20000000000000000000000055200300000000000000020300 23303235013251501
I dissagree when people say that all-frost is best because if you have never noticed, blizzard NEVER crits... even iff you go 5/5 on iceshards, it only works on frostbolt/icelance basically (sometimes frostnova, but not enough extra to make much of a difference)

here's an example of the flamestrike-coc combo ( http://www.youtube.com/watch?v=iyig-3brcnk )
basically it's nova, flamestrike, spam CoC when flamstrike is done, rinse, repeat
it works wonders..... trust me