Technical issues in Heroes IV.

Perhaps the problem lies in the hardware. For example, the behavior of the same game can differ on different computers. In particular, on one of my machines, some maps in the editor do not open (an incompatibility of game versions is indicated), while on another, the same maps open without any problems.
A netbook, as I understand it, is a reduced version of a computer for office work. Therefore, the problem might be with DirectX, which is installed separately, or with some other additional components that are installed.
Try searching online for the game's name (2 or 3 add-ons - it's better not to install the main version, as it slows down the game significantly, and even patches may not help). You can find a good build on a torrent or somewhere else. And it is desirable to specify what exactly is missing for the game to run.