Excel 2003 problem

My mouse sticks when I “left” click on any cell within my workbook. If I open a fresh workbook I can right click all day, but as soon as I left click it’s almost as if I’m holding down the shift key. I’m not able to click on any of the menu options, and the only way to stop it from scrolling around the screen is to go to the start bar and right click and close. I’m on a Dell latitude D600 w/ WinXP and Office 2003.

Thanks in advance for you help!!