Without a windows 7 product key, windows disables functionality.
This could be because of corruption of the license store, or because your current trial of windows has expired. To fix this first recreate license store. Press start, then type cmd. Right click on the application that is found, and select Run As Administrator.
Then type net stop sppsvc (this will stop the Software Protection Service)
rename tokens.dat tokens.bar
Then restart the Software Protection Service
net start sppsvc
This will then have reset your activation. You may be asked to enter your key in. If you do not yet have a key then you can temporarily use a default key to give you a 30 day trial. However you can not enter a default key using the activation window as it immediately tries to activate the code, which will obviously not work. So to enter the default key close the activation window, again open the command prompt (cmd) with Run As Administrator. Then enter the command: slmgr /ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX
Substitute the X marks with a default product key that matches your version of windows below.
Ultimate – D4F6K-QK3RD-TMVMJ-BBMRX-3MBMV
Professional – HYF8J-CVRMY-CM74G-RPHKF-PW487
Home Premium – RHPQ2-RMFJH-74XYM-BH4JX-XM76F
Home Basic – YGFVB-QTFXQ-3H233-PTWTJ-YRYRV
Starter – 7Q28W-FT9PC-CMMYT-WHMY2-89M6G
After a reboot windows will then enter into its 30 day trial mode, enabling full functionality within Windows.