Reinstall of CS6.0

A long time ago I had Premiere Pro CS5

I bought the "interim" version CS5.5 because it came with a free upgrade to CS6

CS5.5 came with a serial number... which I entered in a text file and copied to an external device for security

I never installed PrPro CS5.5

When I installed CS6 I had to enter the CS5.5 serial number

You may not remember it, but Adobe always gives a unique serial number

If you registered your products at purchase, your serial numbers are recorded in your online account.   Log-in below.

https://account.adobe.com/products

That said, CS6 is 10+ years old, discontinued & unsupported.  It won't install on newer computers due to its advanced age and incompatibility.  This is a good opportunity for you to get current software.

MODERN OPTIONS:
Photoshop Elements or Premiere Elements (no subscription needed).
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Have once bought a CS5 upgrade

This CS 5 didn't have any serial nummber

 

Could someone give me some help?

By @Michael28388368fk0u

In order to install an upgrade from CS5 to CS6, you need the CS5 serial number as well as the CS6 serial number.

To upgrade from CS4 to CS6, you need the CS4 serial number as well as the CS6 serial number.

If you purchased a CS5 upgrade from Adobe, you would have been given a serial number for it.

Check your Adobe account:

https://helpx.adobe.com/download-install/kb/find-serial-number.html

if you purchased a cs5 to cs6 upgrade, you need both cs 5 and cs6 serial numbers.  if you purchased a cs4 to cs6 upgrade (which i don't recall being possible, but if it was), you'll need both those serial numbers.

It might also allow you to select CS4 as your qualifying product.

Or, you could use the CS5 serial number if you can find it. Not sure why you wouldn't have it, just because you never installed it?