Yup, however though, I found a way I can actually play it. Just click on [Load Game] > [Campaign] and choose which ever mission you want. there's one draw however, it seems zoomed in and there are two black bars on either side of the screen, everything feels crammed.

Edit: I'm not sure but this may be the problem as to why I need a serial number. So when I first downloaded SIII it was on my PC, so I moved it and is now on my laptop. Could this be the problem?

Also, can I download the game again but this time on my laptop without buying a new copy?

Thank you.

Yes. You can install this game on all your PCs without buying a new copy.

Not really. It shouldn`t ask for the key more than one time.

Hmm, would the problem be that I didn't download DirectPlay? If so where do I download it?

You should do all what is written in the workaround. So yes, this could be the problem.

Kekoas:

"For Win 10 64bit
Ok, so I read that renaming winmm.dll works, and it did for me. I just opened the folder location and change it to x-winmm.dll.
Win 10 will then ask you to install DirectPlay "feature". I clicked install, and started the game up. First time I played it it was asking for a serial key, so I closed the game, restarted and it stopped asking.
Other than that, seems to be working fine. Only thing missing was the music. All SFX and voice were present."

A developer on github posted today a fixed winmm.dll which works on Win10 too. Just download the file called "fixed_winmm_win10.zip" from https://github.com/Tarvis451/ogg-winmm/releases/tag/v1.1, unzip it and copy all the DLLs to your games folder by overwriting the old ones.
This way S3 starts up on Win10 and plays the music too :)

I had the same issue and have come on here to find out how to fix it and although I've replaced the files, I got Error! message saying a DirecrtDraw Error DDERR_GENERIC occurred at CSurface::DDLock

Before replaing these files this I had an error message saying:

CAppNotActiveException Application is not active at:

And I have no clue what any of it means

This kind of helped, but kind of not. Now i get a runtime error saying "abnormal program termination" instead.