Hiya madness99 and welcome to the forum
Are you buying the game from the official site at www.shipsim.com ?
If the file is stopping half way through, you won't be able to open it, it's incomplete. The download needs to finish completely before you can open it
If you have problems with downloading it, may I suggest using a Download Manager, GetRight is a good choice
Regards.
DJM.
Edit: When you next reply to this topic, I will change the title to make it more appropriate