I have an ESP Horizon NT-II which I purchased quite recently. But since I received the thing there has been buzzing noise with it (you know, the damn static humming noise that happens to all guitarists that change in volume when you touch any metal part of the guitar), and the volume knob produced a lot of scratchy sounds when turned.

After 2 months now, the volume knob problem has become worse as I experience signal/volume loss at almost all the position of the knob. Full volume and around 1/4 volume give out normal sound (but of course with the noise that's been there since the beginning), the rest is dead silent with a clean tone and produces a nasty loud humming noise if I turn on distortion (the noise goes away/return to the normal noise as it was before when I turn to the working positions).

Since I don't know about electric stuffs I had this guitar looked at by a guy who does and he said there is nothing wrong with the wiring. Everything is properly grounded so I start to think that is there any chance that the faulty/broken volume pot is the culprit for the humming noise since the beginning? It is a push/push coil tap volume knob btw

PS: My other guitar works perfectly with absolutely no noise whatsoever so I don't think there is anything wrong with my amp or my cable.
Yes, dirty/faulty pots can produce a 'gritty' sound when they're turned. An extreme buzzing sound could be explained by improper grounding...

Did you get the guitar new, or used?
it's brand new but it got shipped from halfway around the world so I guess some craps happened on the way.

What I'm saying is that is there any chance that the buzzing sound is caused by a faulty volume pot but not improper grounding?
I imagine it could, but it would be a different kind of buzzing than what I read it to be.

Are you in the position to take it a shop to have the pot checked out/replaced? Or can you do it yourself? Should be a pretty easy, cheap fix.
I wish I could do it myself , but I have absolutely no idea how to work with guitar's electronics. I can set up a guitar nicely with ease. But when it comes to electronics.....

I should take it to a shop. But there is nothing near where I live either ). Saving money to get this fixed . It sucks ass when you live in a city with no guitar maintenance shop
its your pots, take em and get them replaced at your nearest shop. A good place will charge you $25 plus the price of a pack of strings for it, its a pretty minor upkeep for pretty cheap