Acer Extensa 2900E

I have an Extensa 2900E notebook running Windows XP Pro.

It is producing typing errors in that it seems to stop during typing and
drop some letters intermittently. For example, if typing "last mover" it may
drop the letters and space from a to m and the screen displays "lover". The
errors are present in all types of software where text input is needed.

I thought that it may be a keyboard fault so I connected a USB keyboard to
see if that fixed the problem, but am experiencing the same problem with it.

Apart from that the notebook is working well.

Does anyone have an idea about what may be causing the problem and how to
fix it?

Thanks,

Ian