Can't use ESC key in vi?


When I used vi, I typed ESC key to return the command mode. However, it can't work. I tried to use ctrl + option + ESC key,. it works fine for force quit. Therefore, my ESC key doesn't have problem.

Why this key can't work in my terminal with vi?
I use Pismo 400, 320 Ram and Mac OS 10.04

Thanx for helping
I tried to use root to login to X and used Terminal with vi. The ESC key worked fine. When I use my local name login and used ESC key for vi. It couldn't work~~

I want to kill the vi or terminal preference in my local preference folder. However, I'm not sure which one is for vi~~