Please try this:
1. Open BlueSoleil 8, Display Classic View;
2. Click "Show Menu" button in the upper right corner. Then "Help->About BlueSoleil";
3. The SN can be found here;
Or
Check the Activation e-mail, you would just find.
If the e-mail was lost, please send the "Order NO." to store@bluesoleil.com.
Best wishes~