So, I bought DG this morning, eager to play, i deleted all the mods that would conflict with it. I'm telling it to show that the problem is in the add-on. So whenever i activate DG to load, and start the game, loading the latest(basically, any) save, I spawn in the sleeping giant Inn beside the naked courier who says: "I have important deliveries to make, no time for chatting!". Nothing else happens. When i try to exit the inn, i get the endless loading black screen(just with level progress bar).

So? Please help?

you said " deleted all the mods that would conflict with it"
try disabling ALL esm files other than dawnguard, not just those you think would conflict with it

by deleting all those mods, you may of infact curropted ur game

Yep, i disabled all of them, and the game loaded... I was hoping i won't have to do this routine to play the game, but it's obviously inevitable. So, now i will have to find the "bad" mod. Thank god i have only 20 of them.

Given, that Dawnguard has huge potential to conflict with:
- any mods, that are only disabled, and not completely deleted from the Data folder, and
- any loose files in the Data folder, that may remain after failing to completely delete a mod, and
- any mod-related data, that has been baked into your save file and cannot be removed by any means currently available,
you can only absolutely reliably play/test Dawnguard, if you use it with a save that has never seen a single mod.

This will probably be the situation until all mod creators are totally familiar with the impacts of Dawnguard, and know how to take it into account when creating and updating their mods.

So i tested, and Unlimited Tamriel mod is incompatible, it seems.
I will continue, and tell if there's any other