i bought a dell inspiron 15r 5537 with windows 8.1 preinstalled almost a year back. but now its showing that my product is not activated.. how can i find my product id and key for windows 8.1..

The product key is  usually on the bottom of the case of the Laptop.

If that is missing then you download and install Belarc Advisor to find out the product key.

You can use this tool to find the embedded key

https://neosmart.net/blog/2014/windows-10-embedded-product-key-tool/

Why you need to is another story.  Have you made any changes to the system?  Did you buy it from a computer maker?

Hi,

For the preinstalled Windows, you should contact the manufacturer to help reactivate your Windows.