HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

I have several problems at once... I'll start in order.
Windows XP, ADSL connection via a D-Link modem. Internet speed is 256 kbps. Latest version of Heroes, HotA, SoD with patched executable, complete Russian collection...

HoMM3 HD – the mod does not affect either the installation of your game (all your files in the Heroes folder remain intact), or the internet connection settings; only the game interface changes. All problems are related to the basic game installation and the operating system (network settings, as a rule).
You can find some information about the problem in useful links. You need to install version Heroes 3.2 first. And then – the mod.
And don't do

any strange manipulations

:)
The described problems are presented somewhat chaotically and vaguely, and they can be discussed with one of the players on ICQ if the available published information is insufficient.
p.s. Regarding difficulties with connecting/data transfer in Gameranger, it was found that when updating the antivirus, the program core (system functions) may also have been updated (almost all antiviruses today implement firewall functions; and vice versa). Therefore - roll back updates, or you should look at the functions of antiviruses.