But after sometime system will ask for windows activation key, If you will not activate your windows, you can not access properly your work on your desktop/laptop. in this case you have to purchase product key for activate your windows.
But Do Know that you can activate Windows with purchasing any Product key...?
Yes you Can activate your windows free of cost, Just Download a Software (don't worry, I'll provide link for download software) and follow steps.
Watch Video Here:-
Extract Downloaded Software.
Open "Windows 7 Loader eXtreme Edition v3.503"
Software will Open, and wait for Restarting 3 or 4 times.
Download File Here