The most common reason a Nuendo Live 2 activation code "doesn't work" is using the wrong software to activate it.
Enter your Download Access Code (DAC) here. This will convert the code into a license tied to your account.
Are you seeing a specific (like "Background Service Unavailable") when you try to launch the Activation Manager?
Since Nuendo Live 2 uses identity-based licensing, you don't "lose" your code if your laptop crashes.