On my old computer I got Cortex Command. It was fun yeah, it had bugs (Which I understand since of its current place) and I loved the physics. 9/10. Now, since my old computer was, well, old, and had to die, I got a new laptop. But, since of my new computer, I apparently need to pay again or it seems so. Is there any way that I can get the game on my new laptop since I already paid for it or no? I would be somewhat satisfied with the demo, but the link to it leads me to a website saying that its having a sale and is free and leads me to actually buying it. So the demo isnt an option. Please help me

Do you have your old key and email? If so, head to licensing.datarealms.com/licensing and enter those as your username and password (email being username). You'll then be able to download the newest versions.

If not, then you'll have to contact support@datarealms.com and try to work something out.

Ok, but, if I want to play the demo until I have the time to do that, where can I download it?

There's no demo for versions beyond b23, as there isn't any DRM on the game itself.
b23 can be found at this link.