Plants VS. Zombies corrupt download

I've had this game for a very long time, I bought it back on a different computer.
Do to the computers age, it's started having issues, like the screen not working (it's an older laptop).
I have taken the hard drive out and transferred my files over. With this game though, it says that I have a corrupt download. Is there a way that I can uncorrupt the download? I don't have another way of getting the game again without rebuying it.