In this case you’ll need to open the Control Panel (without a mouse, you can do this by pressing the Windows key, waiting for the Start menu to appear, then pressing C). From here use the arrow keys and Enter button to select Accessibility Options, and then use the arrow and Tab keys to select the Mouse tab and tick the box marked ‘Use Mouse Keys’.
You’ll now be able to use the numeric keypad on the right-hand side of your keyboard to move the arrow, and the Enter key to simulate the mouse button. You’ll probably want to change the settings in the same menu to increase the Top Speed and Acceleration settings, else the arrow movement may be painfully slow.
(On some computers, you may be able to turn this option on and off simply by pressing the left ALT key, left Shift key and Num Lock key at the same time.)