Reinstalling without the key means Windows XP will enter a 30-day "limited functionality" mode.

The genius of the Recoverer and Discoverer was not in brute force but in its elegant reverse engineering. Instead of relying on a static list of leaked keys, the program is believed to have cracked the underlying algorithm Microsoft used to generate its keys, effectively building a mathematical model to create infinite, valid product keys from scratch.

If you are trying to find the deployment identity key used for a custom install disk, you can often find it saved in plain text directly on the disk itself. Recovering a Windows XP License key - Super User

Remember: A recovered key is a second chance for your machine. Use it wisely, legally, and keep the legacy of a robust operating system alive—safely.