New hard drive and windows

[mohi_18]

My older hard disk is not working.I dont know my windows 10 key. So have i buy to new windows for replacing hard disk? I dont know much about these things. Please help.

 

[RealBeast]

You can simply do a clean install to a new hard drive, Microsoft has your key saved on its authentication server since you already upgraded with them. When you go back onto the Internet after the install to authenticate, they will do it automatically.