Whoa....this thread escalated quickly. Not my intention. Really sorry that I am late for making my response here >.<!
Anyway.
The activation key is working now. Not sure what happened.
I went into my account in rpgmakerweb.com, clicked on that MV preorder confirmation, and the copy-pasted the steam key into the blank page under email address in the activation page.
That didn't work. It said: "Oooops....blah blah blah" - basically told me that the activation key is wrong.
And then I wonder if removing the dashes would work, but it also didn't work.
I checked the activation key over and over again (after copy paste before clicking on "activation" button), and nothing worked. I made sure the key entered into the blank page was indeed the steam key provided and after some times, I gave up, typed in the activation key codes directly (with dashes) instead of using that copy paste technique. And it works...............
Not sure what really happens there, but I am glad that it works in the end. I almost wanted to reinstall my windows 7 for this!~~