Here is how:
1. Press Left Alt + Left Shift + Num Lock Button and click OK in the dialogue box that appears.
2. In your Taskbar, a mouse-like icon will appear. Double click it and under "Mouse" tab, make sure that the "Use Mouse Keys" is checked.
3. Also ensure that the Num Lock is ON (i.e. the light must glow).
2. Now with the help of Numeric Keypad e.g. (Press and Hold the following Keys)
7 8 9
1 2 3
For normal click, press 5
Interesting, isn't it? You can also change settings under the "Mouse" tab in "Accessibility Options", by clicking on Settings