An install of Windows 7 without an activation key allows for 30 days of usage. This can however be extended up to 120 days by using the following slmgr (Software Licensing Management Tool) command to rearm or reset the 30 day trial.
(Remember to run this command, you must right click on cmd and select “Run as administrator” for this to work) However this can only be done up to 4 times. You can view the number of rearm counts by using the command which displays the current license information:
Notice the second to last line shows that I only have 1 more remaining rearm, after which the software will expire. However there is a small trick that allows you to reset the rearm count back to 4. To do this you need delete the registry key which contains the Last Rearm Time, however this key can not be deleted or modified during a normal user session. To delete the key you will need to run the following commands in the windows recovery console.
reg load HKLM\MY_SYSTEM "%~dp0Windows\System32\config\system" reg delete HKLM\MY_SYSTEM\WPA /f reg unload HKLM\MY_SYSTEM
To do this save the above commands to a .bat file ‘reset.bat’ to the C:\ root folder. Restart your computer, pressing F8 to get to the Advanced Boot Options. Select the option to Repair Your Computer. Select your keyboard input method. Login with your login details. In the System Recovery Options menu, select Command Prompt. Now type in C:\reset.bat. (If it says “‘C:\reset.bat’ is not a recognised as in internal or external command” message, then it may be because the C Drive is bring used as a recovery partition. Try again using D:\reset.bat) If successfully you should get the message “The operation completed successfully”. Next reboot your machine.
After rebooting you may get a message stating that this product is not genuine. This can be ignored. Running `slmgr /dlv` again will confirm that the rearm count has been increased again, thereby giving you another 120 days worth of windows use.