Where I can find my System ID ?

If the program is created by a customer, we cannot help you. The System ID in XLS Padlock is a unique identifier automatically generated from your computer’s hardware components. It is used when our users enable hardware-locked activation keys so that a key will work only on that specific machine. The System ID is automatically displayed when you start the program.
If not, then you don't need one.

Thanks for your Reply.
One more question, If I go with your this "XLS Padlock" for my excel program. Is there an option to disable/ de-activate the previous Activation Code and Generate new for the same machine ?

No, because you must be the author of the workbook app in order to generate keys for that app. Otherwise, anyone could just download XLS Padlock to make keys for any protected workbook. That would be a major security failure.

Thanks for your reply.
May be I didn't explain well or you didn't get my question.

My Question is, If I purchase your "XLS Padlock" for my Another excel sheet program (not the one about I mention above), and I'm the Author or Owner of the sheet. Now I issue an Activation key to someone for his system using "XLS Padlock". Then, Is there an option to disable/ de-activate the previous Activation Code which I issued earlier and Generate new Activation Code for the same machine ?

Thankyou