This may work, when you don’t have genuine license but you still want to use evaluation period of Windows OS. Basically Microsoft gives 90 days evaluation period without purchasing any key to use Windows OS. If you need, then you can try out this. It is very easy.
Step 1: Click Start, and run Command Prompt under administrative mode.
Step 2: Type
and then press ENTER to check the current status of your evaluation period
Step 3: To reset the evaluation period, type
and then press ENTER
Step 4: Restart your computer. Then your evaluation period of Windows will extend for 60 days more. Hurray !!!!