Hi I have C6 creative suite on disk. It has been transferred to my new desk top. I have the serial

in any app, click help > activate.

Try the offline activation as described as Solution 2 in the linked document.

https://helpx.adobe.com/creative-suite/kb/serial-number-validation-launching-cs6.html

But be aware: if you have reached your activation limit and you don't have any chance to deactivate an older installation you're out of luck. Adobe has stopped the support of CS 6 products and the resetting of the activation counter isn't possible anymore.