Windows 10: how to recover windows product key that went away with fried motherboard ?

so a few months back my Dell laptopwhich came with preinstalled licensed Windows 10 motherboard got fried for unknown reasons and I had to replace the motherboard. I had to reinstall Windows 10 on my laptop because it got laggy after the repair. now the Windows copy is not licensed and there is an annoying watermark at the bottom right side of the screen and some customization features are locked. I had an email id registered with that licensed windows copy. is there any was to product key back?any help would be really appreciated

:)

 

Recovering product key from unusable PC

I’m currently in the process of building a new PC. I have all the parts needed to start, but I wondered if I could recover my old Windows 10 product key. Most of the answers I’ve seen requires me to get on my old PC. Unfortunately that isnt an option for
me as my motherboard fried and I can no longer access it. If there are any options such as calling Microsoft Support or literally anything to help me would be much appreciated.

 

Downgrade to windows 10 home after motherboard change.. no product key

I had windows 10 home with existing product key, harddisks got fried.

I changed the motherboard, installed new harddrive, but accidentally installed windows 10 pro.

Can't activate home license on pro, but i can downgrade to home with an existing product key. Unfortunately, i don't know what the product key is.

I don't want to do another re-install.

moved from: Windows / Windows 10 / Windows settings

 

Finding the Windows Vista product key

Allright,I've tried the Hirens BootCD on USB drive and it works like charms.unfortunately,none of the utilities included on it helped me to recover the vista product key..but thats not important anymore,cos I just did a fresh install in the end..everything works fine,but a new issue arise.
DVD drive not recognized in my computer under Vista
tried few things but no results..what do you suggest guys?