|Apparently your model was probably made in 2005.|
Examine the keyboard carefully and make sure no keys are stuck in the down position.
Look in your Owner's or User's manual - many laptops have a key or key combo that toggles what the behavior of pressing the keys do - you may have pressed that un-intentionally.
If that doesn't help your keyboard may be malfunctioning. Keyboards on laptops are are a frequently replaced item, and not all that expensive. Replacing them is usually easy to do yourself once you find out how to remove and replace it. Lenovo /IBM may have a Service or Maintenance manual you can look at.
You could try a PS/2 keyboard plugged into the PS/2 port, or a USB keyboard, but you may need to consult your Owner's or User's manual regarding enabling it while booting / disabling the built in keyboard.