Hi !
IMHO, the lack of interaction while you were involved with school could be the beginning of this. As my friend Noodles pointed out, IRNs need a lot of interaction with people in order to remain tame. Ringnecks are famous for this, returning back to an almost wild state if they are not played with and interacted with almost daily. The other factors mentioned could also be exacerbating this. Most IRNs HATE being touched. A lot have fear of hands. Of course, these are generalizations, and if nothing else, all parrots are individuals with their own personalities, likes and dislikes.
Start from scratch, as if you just got him as an adult bird. Spend a lot of time just sitting as close to his cage as you can ( without upsetting him), and read out loud to him in a soft soothing voice. Parrots love being read to. A good thing to read is the "I Love Amazons" thread over on the Amazon forum, at the top. TOns and tons of great info, and applicable to ALL parrots. another thing to do is to drop a small treat in his food bowl EVERYTIME you pass his cage, maybe even have a special small bowl just for that.
Parrots accept change slowly, at an almost glacial pace, especially when compared to our quick adaptable monkey brains. Patience is the key word. You can explore target training with him, in cage at first. Look that up online and here on the forums.
Assure yourself that the other conditions mentioned above by Noodles have been addressed.