Square Mouse Cursor

Dear Sir,
I have PIII, 128 MB SD Ram, 20 GB HDD, Norton Antivirus Professional, Logitech Scroll Mouse and win 98se insalled on my machine.

There is very strange problem with the mouse cursor. The mouse cursor ramins normal for some time. But after 1 hr or so when i scroll down/up in word documet the mouse cusor becomes square. It only comes to its norman condition after restarting the pc. But after some time same thing happens.

Installed driver also. I have scanned by norton no virus found.
what is the problem please help me.