Automatic scroll up the page. HELP !!

I have a Toshiba Portege 3020CT Notebook and using external PS/2 Keyboard and Mouse at the same PS/2 port with the PS/2 spliter cable.

Now the problem is the when I open the Word 2000 or Excell 2000, I will having one problem that’s is when I page down the pages it will automatic scroll the page up to top.

Why this can happen??? Please Help.

Thanks you.