SureAI

The main quest makes me go to him, and he asks me if i want to improve my skills, but then his menu is blank and all i can do is use the persuasation menu

From what I've read on various forums, the training menu is blank when you don't have enough money for training. How much money is "enough" is a mystery. Silly, I know.

or u reached 90 at that skill

No, Lathorius has nothing to do with the mainquest.

Yea, I figured it out, the quest indicator took me to him, and then it finally switched to some other lady. Thanks.

But now I have a different problem, on that Island where I'm suppose to hunt treasure, nothing seems to be there.

It's there. It's just that hidden treasures in nehrim tend to be actually hidden, instead of lying in plain sight like oblivion.

edit: lol if you think that's bad wait until you hit the arcane sanctum. I swear to god, I must've tramped around in the same patch of bush for half an hour before I found the trapdoor to one of the caves.