I do not know that Excel Automatic Calculation problem has been faced by you or not. But i have faced this problem in Microsoft Excel which i want to share with you. This problem arise when you have fixed formula's in Excel for your fast or accurate working and Calculation of formula does not work. In below picture, a calculation has been shown for 15 x 3 = 45 (right) and 15x 15 = 45 (wrong). These all depends upon the setting of Advanced Options as shown in below picture in Microsoft Excel 2007. Due to any reason, if you have selected Manual of Advanced Options, Excel stops automatic calculations.
(care is required while working in Excel)