“Heroes of Might and Magic V: Tribes of the East”

I don't understand something. I bought Tribes of the East, and it says that it doesn't require the original game to run, but it won't run without the disc?

You're confusing the need for the original game and the need for the game's disc:)
The fact that the expansion can be installed even if you don't have the original Heroes V means that you don't need the original game to run it. But you still need to put the disc in the DVD drive:))