IDM Serial Number Problem

Hello, sir/madam

I'd like to ask about serial number. Why it still keeping on asking me for it. To be honest, I really had no idea what is it about or even know what was the serial number for my computer as well because after my father took my computer to restore new program at the computer shop, IDM has already existed in my computer. Can't the app give us another serial number or what? I can't download Music Video and even MP3 because of it now. So, please. I hope you will give me a very perfect solution.

Thank