Solved Office 2010 Missing Product Key Error

Office 2010 Missing or Prompted for Produck Key

This issue is most likely related to cannot open files after installing update. 
Cause:  This issues is caused due to Windows update KB2589275 
Missing Product key

Check for multiple Office installations. If there are multiple installations of Microsoft Office 
installed follow these steps:

1. Go to control panel.
2. Click on all programs and select uninstall programs.
3. Select Microsoft Office Click-to-Run 2010 and click uninstall or remove for windows XP.
4. Select for Office 2010 MSI-based suite and click change.
5. Select Repair, and click Continue. You may be prompted to restart the computer after the repair.

If there is only one Microsoft Office on the computer.
1. Right-click the file you want to open.
2. Select Open with and click on Choose default program.
3. Select Microsoft Office Client Virtualization Handler.
4. Select the Always use the selected program to open this kind of file check box.

If you have any question feel free to comment below.