I purchased this game shortly after release and haven't played for years. Decided to come back and check it out again. I log into my account and I only have the option to buy it not download it. What happened?
Might be all the updates in the meantime.
The Launcher should prompt you to download new version of it self though.
Try logging in to frontierstore.net and check your account/My downloadable products, download the client installer and run it.
If all else fails, the support should be able to help.