You could try uninstalling Office while in selective startup mode using the utility mentioned below.
Then also reinstall Office while in selective startup mode.
To boot your machine into selective startup mode you will need to launch msconfig and disable all 3 party services and startup options.
To do this, you can do the following:
+>Click on the start menu and type MSCONFIG into the quick search box.
Launch msconfig.exe.
+>Within the msconfig dialog, click on the Services tab, then check the box to Hide All Microsoft Services and then click the Disable All button.
+>Then click on the Startup tab in the msconfig dialog and click the disable all button.
+>Click Apply and Ok.
+>You will then be prompted to reboot your machine.
Once the machine is running in selective startup mode, first make sure any antivirus software you have on your machine is not running (it shouldn’t be, but I would recommend checking and
if it is you will need to disable it). Next uninstall your Office suite by running the Fix It utility for your specific Office suite in the KB article below:
290301 - How do I uninstall Office 2003, Office 2007 or Office 2010 suites if I cannot uninstall it from Control Panel?
http://support.microsoft.com/default.aspx?scid=kb;EN-US;290301
After doing this, you could then try and reinstall your Office suite, while still in selective startup mode.
Once Office is reinstalled, I would recommend testing your Pivot tables again.
If they work, then boot your machine back into Normal mode and test there.
Best Regards,
Nathan Ost
Microsoft Online Community Support