error during installation

I downloaded the full version of The Sims 3 through Steam, but when I click to open it, I simply get the message "error during installation," and when I click to verify the files, it says there are corrupted files, but they aren't being repaired. I don't know what to do anymore... I haven't given up yet only because Steam doesn't offer refunds to credit cards in my country, and I would lose out.