I have a new windows 8 Laptop I installed Office Professional Plus 2010 successfully. However, office documents attached to email, and existing files will not open (surprisingly they will preview) without a dialogue box requiring the licence key. The licence key already accepted on install is now rejected! 

Windows 8 is horrible. The cursor movement causes unexpected switching between tiles. Everything is counter-intuitive and hard to find.

My worst nightmare. Productivity shot to pieces.

Please check if you have any other editions of Office that might have been pre-installed on your laptop, if you find it, uninstall it and check this behavior again (after the uninstall, you might need to repair your own Office installation to have it function).

If you couldn't find anything, I'd suggest to uninstall the current Office installation by follow the instructions in the KB article: Uninstall Microsoft Office 2013 or Office 365, after that, try to reinstall Office and check this behaiovr again.

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For the cursor movement issue in Windows 8, I'd suggest you to visit the Windows forum in Microsoft Community: http://answers.microsoft.com/en-us/windows/forum/windows_8