The original key for your Spyder product is usually found on a label stuck to the packet in which the software that came with your device is supplied. It's a very good idea to keep a copy of this key somewhere else as well.
If you lose this key, we can't help you I am afraid. You will need to visit the support section of www.datacolor.com and request they issue you a new key.
(They may request proof of purchase - If you bought you device from us after February 2009, just log in to your account and re-print your own invoice. If you bought your device before February 2009, please use this form to request a copy of your invoice).