Excel workbook closes without warning

[kafka]

I have a workbook containg a number of worksheets and a large amount of data as well as macros and many formulas. Often when I am in the process of adding or deleting data Excel freezes and eventually closes down, which results in my losing all the work I have done up to that point. I have uninstalled and reinstalled Office but this didn't help. I am using the venerable Office 2007.