Q. I'm trying to install Office 2010 but it tells me that my key can't be used because a trial was most likely previously installed. What's wrong?

A. There are often remnants of Office left on a machine even after an uninstallation. You can visit this Microsoft site to download a tool to uninstall Office 2003, 2007 and 2010. The tool is the safest and easiest option, but you can also go through and delete all of Office's various registry and file locations:

  • Delete HKEY_CURRENT_USER\Software\Microsoft\Office
  • Delete HKEY_LOCAL_MACHINE\Software\Microsoft\Office
  • Under Program Files or Program Files (x86)
    • If it exists, rename "Microsoft Office" to "Microsoft Office OLD"
    • If it exists, rename "OfficeUpdate" to "OfficeUpdateOLD"
    • If it exists, rename "OfficeUpdate14" to "OfficeUpdate14OLD"
    • If it exists, rename "OfficeUpdate12" to "OfficeUpdate12OLD"
  • Delete everything in %temp% and empty the recycle bin
  • Reboot the machine
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