Do you still have the product key? If so, download the Origin client at http://www.origin.com/download , log in, and redeem your product. You will have full access to the digital download of the game.
If you no longer have the product key but you still have your old PC, you may find your product key there. Find DAOriginsConfig.exe in the installation folder under 'bin_ship' and see if the code is displayed under the 'game' tab. It may not be there, however.
If all else fails, the game is currently on sale on the Humble Bundle along with other EA games. You can pay whatever you want, even if it's just one dollar, which goes to charity. You will get five games for $1 plus four more if you pay $5. https://www.humblebundle.com/
