Corrupted file?

I downloaded the windows version, played a few excellent hours and something weird happened to the application.

Now I cant start it up and I can't download a new copy from the backend because my key has already been used, can you help?

Having searched through my laptop I can find the .exe but no attempts can get it to run. It also doesn't appear in my downloads.
I'm a bit of a rookie when it comes to computers but it should be there somewhere right?