I just recently installed the FSX Demo on my laptop to see if I can get FSX working again.

 

Is it possible to activate FSX into the full version from the demo? Or do I have to have the DVD to fully install FSX? If I can activate the demo, how do I do it?

No, you need the DVD (3 DVDs in the case of FSX Gold) or you can buy a full digital download for PC from Xbox Marketplace.

 

http://marketplace.xbox.com/en-US/Product/Flight-Simulator-X/66acd000-77fe-1000-9115-d8044d530935

Or You can get the Gold edition on Ebay for a lot cheaper and new.

Or, I could just look for the dvds I already own... for free.

The Gold Edition (the fullest and most complete edition) is super cheap on Amazon... I think it's like $17.

I have FSX Gold but when I copied the files of both cds it would take a long time so I thought I'd try to see if I could activate the demo product into the full version.

It's not possible because demo contains only small part of full FSX content.