Technical issues with Heroes III.

I have the following problem: when starting a multiplayer game on one computer, in the name input window, the "=" character is constantly (spontaneously) entered, with a frequency of 2-3 seconds. It looks like a key is stuck, but there is no actual key sticking, neither on the system side nor on the keyboard side, only in the game. I tried reinstalling the game, and I recently reinstalled the system. I tried installing both official and pirated versions of the game and different versions (except for "In the Wake of Gods"), but the error persists. It wouldn't be a big deal in principle, but because of this error, the hero's turn is reset directly in the game on the global map, which is extremely annoying. Try pressing it about ten times so that it finally reaches point "B)". Has anyone encountered this problem? The laptop has a dual-core processor, Windows 7, and otherwise, there are no special features.