Edit2: The issue seems to originate with Games Explorer (GameUX.dll), a worthless and very poorly-made holdover from Vista that was apparently meant to be used to update games. There are pre-made registry edits that can block this nuisance. They may have to be re-applied after installing a game.
https://www.gog.com/forum/general/old_games_not_launching_and_eating_100_of_the_cpu_on_windows_7/post61
or
https://www.gog.com/forum/general/old_games_not_launching_and_eating_100_of_the_cpu_on_windows_7/post68

Edit: Got it working by closing the game exe in task manager and booting the game again while rundll32 is still running. rundll32 still has to be manually stopped after I'm done playing. This has to be done every time I play the game, apparently. Now this raises the question of what I can do to get it working properly again without the annoying workaround. It was working normally before.

Windows 7 64-bit. Stronghold Crusader Extreme HD works normally but Stronghold HD and Stronghold Crusader HD both fail to start. Trying to start them only results in large amount of CPU resources being perpetually eaten up without actually starting the damn game. I have to hunt down and stop rundll32.exe in the task manager order to terminate it.

I have same problem, nothing started and rundll32 just eat CPU, thanks for tip with kill and start game exe again while rundll32 is still running

Thank you! This fixed the problem.

If only. Now that I have an idea what to look for, some searching showed this issue has been known for several years. Apparently this has been fixed in later updates to Windows 10 but not Windows 7. Gee, I wonder why.
https://answers.microsoft.com/en-us/windows/forum/windows_other-gaming/windows-7-game-explorer-interfering-with-game/efd39c74-cfab-4c2c-b6c5-834b8849a1b3

Just remove the game explorer then.