i just recently downloaded heroes 3 complete edition but when i went to the single player it said i needed the disk in to even do the campaigns can someone help?

Every now and then I read people stating the GOG versions are asking for a disk, but I've never encountered anything like this.

I can make the usual recommendation of not installing these games in the Program Files (x86) folder (for Windows Vista and 7). If you did then re-install in a different folder. If you still have this issue, you might want to have this run as administrator or try compatibility mode with XP or even 98.

This is a common issue for all the downloaded versions of HoMM3.
The solution is usually to just put a random cd in your disk-drive. Most people that never see this issue usually have a cd in already. :)

Running the games as an Administrator (Right click the shortcut --> Properties --> Compatibility --> Run as Administrator) should stop the CD message :D

Not to resurrect an old thread, but I had this problem yesterday and managed to get it properly fixed.

From what I read (and this worked for me) this occurs if you have previously installed a disk version of the game.
The problem is that when the old version is uninstalled, it doesn't remove the registry data.

If you open regedit (press Windows Key and type "regedit" and hit return if you're on Windows 7/Vista) and search for "New World Computing" you should find some leftover entries, if you delete those, this will fix the problem.

Hope that helps.

Try uninstalling the game, deleting any remaining keys in the registry, then installing it again.