Windows XP gives you the option to work without mouse (with Keyboard only) OR without Keyboard (using mouse only).
These techniques are useful when your mouse is not working or your keyboard not working (any key is working)
Work without Mouse
Press ALT+Shift+Num Lock
You will hear a beep and then you can see windows asking for using MouseKeys. Click OK.
You will see mouse like tray icon if it is crossed like this then press Num Lock again.
Now use the Numeric Keypad to move cursor around.
8 key for Up,2 for down,4 for left, 6 for right
When you want to use the Left click of mouse Press 5. For right click you can this key on the keyboard
Note: The cursor moves very slow but you can speed it up. By pressing ALT+Shift+Num Lock you will see a dialogue click on settings again click settings, and then select Hold down Ctrl to speed up and Shift slow down. Now when you want to move cursor then hold Ctrl and then press any key to move the cursor through numeric keypad. It will speed up now.
Work without Keyboard
Type osk and you will see this keyboard called On-Screen Keyboard. To use any key press Click on any key. Usually this utility is made for mobility impaired users. But you use it if any of your key is not working at a moment.