Game is not setuop to not work with Windows 8.1, however, I was able to play the game through Origin using this solution - https://steamcommunity.com/app/102820/discussions/0/648814845292513057/;
it didn't work for me.
I had already installed the game on Steam; I installed it again on Origin, and repaired it and was able to play with no issues!
To play this game with Windows 8
Install the game on Steam. Make a sims3 account at thesims3.com
and link it to origin. Redeem your CD key on the sims3 site, this will add sims medieval to your origin account. Open your origin and find the sims medieval game, right click it and click repair game. After it repairs and updates, start your game from Origin and you can play.
The game is only installed once to your hard drive, even though you use Origin to repair files and play the game but you install the game with Steam.