My old pc crashed so I used the old stuff to install CS6 again. I tried to enter the same, old code, but now it isn't working anymore. How is this possible?

cs6 works with win 10.

you need to use your serial number.

if you've exceeded your two installations/activations, you need to deactivate on one of your old computers.

if you cannot deactivate your previous installations, contact adobe support during pst business hours by clicking here and, when available, click 'still need help', https://helpx.adobe.com/contact.html and request and activation count reset.