Sorry, i haven't been updating this... (Basically given up)
I tried my Mac, no change.
Tried my Win10, no change.
Tried my another win10 laptop from work, no change.
Tried Firefox, chrome, IE, safari, no change.
Tried to change the transmission power, no change.
Tried changing channel width, no change.
Tried changing 802.11 mode, no change.
Tried to change Visibility status, no change.
Tried 3 computers now and various other FW's. In all respect not going to do that "recovery process" because it's an HUGE pain in the ass. The 5.1GHz works fine, but i cannot change the channel. I just put it in High transmission power and that's it.
But yeah, frustrating and disappointing.
If you come up with SOME thing to try, other than messing with recovery process. (Because i have to remove the router completely out of it's place, wire 5 meter cable, then try it and then put it all back together. It's an huge pain in the ass that takes me about hour to do). Not going to do it. If you have any suggestion other than that i would be pleased to do so, if not. This will be my last D-Link product unfortunately.
Thank you for you help tho! Really appreciate it, and it's not really your fault that i have placed my router in such inconvenient place.