What is the model of Dell and Windows 8.1 Edition?

Follow the instructions here to obtain your product key:

http://dellwindowsreinstallationguide.com/a-clean-install-of-windows/microsoft-product-activation/obtaining-your-oem-bios-embedded-slp-product-key-using-rw-everything-oem-only/

Dell model - Inspiron 15 3000 series

windows - 8.1 pro (build 9600) -> thats what is written .

there is a watermark appearing on the left bottom of the screen - Activate windows

i dont want to reinstall.. and if i do so will the stored contents of other drives remain intact ?? 

i used the laptop as any normal person use it ,even kept on updating it almost daily ,nothing more. But yes i use it a bit more, few days back all of a sudden i observed the watermark on the left bottom of the screen .. 

Let's backtrack a bit - what were you doing that led to the need to activate Windows?  The OEM Dell installation doesn't require activation - it is pre-activated.

I am having this exact same problem. Where you able to solve it?

That link does not work.