Num Lock key is used for enabling the numeric key pad in the keyboard. You enable the numeric key pad manually by pressing the Num Lock button. However, in Windows 8, you can also enable the Num Lock key by default. When you do this, your computer, when it starts will always have the numeric key pad active. To do this, follow the below given steps:
1) Go to Charms bar –> Search.
2) Type: regedit in Search under Apps.
3) Click on regedit icon on the left side. If you get a dialog box asking “Do you want to allow the following program to make changes to this computer?”, click on “Yes”.
4) In the Registry Editor, go to: HKEY_USERS –> .DEFAULT –> Control Panel –> Keyboard
5) Right click on InitialKeyboardIndicators and click on “Modify”.
6) Type : 2 in “Value data” and click on “OK”.
In future, if you wish to disable it then enter 2147483648 in “Value data” and then, click on “OK”.