I bought the game about year ago. and i noted that there is a new version on the webside. I still have my old game key,and the bill, but I don't know where can I get the full game again without pay for it.

Take a look here for the key self-upgrade option.

thanks. I got the key back but i still don't know where to download the full new version game. can any one help me with that?

http://datarealms.com/games.php
Get the one for your OS, then put in your registration key and email on the "register" screen in the main menu.

thank you for your help. but somehow the one I just downloaded is a old version of the game. in the readme it sad "Cortex Command Test Build 17". and it doesn't have the "register" screen in the main menu.
can any one help me with the problem?

Try this link.

thanks, it works