mouse creep ( 9.1 )

Hi, Am running 9.1 on Dell Inspiron 8500. Recently the machine seems to have developed a mouse creep. Oddly the mouse only seems to creep when eg holding down an alt or a ctrl key, or ocassionaly it will creep when using the keyboard. Sometimes it will stop at the edge of the currently active window and at other times creep to edge of screen. ANy thoughts as to weather this is a software or a hardware problem TIA F