I know it's an old question but it seems I encountered same problem when supporting User on my side.
I did a lot of research and I'm gonna try few tricks to solve it tomorrow, just want to share them here, maybe one of those helps:
Solution 1
1.Start>Control Panel>Programs and features
2.Uninstall Compatibility Pack for MS Office 2007
3.Start>Control Panel>Programs and features
4.Click MS Office>Change/Repair>Repair
Solution 2
1.Start>Control Panel>Programs and features
2.Click MS Office>Change/Repair>Add/Remove features
3.Choose Word>Remove
4.Let it finish, then repeat steps 1 and 2
5.Choose Word>Run all from this computer
6.Let it install and reboot PC
Solution 3
1. Go to the thread below and follow step-by-step MS Office removal/re-installation advised by some MS Tech
http://answers.microsoft.com/en-us/office/forum/office_2010-word/word-2010-opens-all-files-in-compatibility-mode/ee1e2be0-ce14-453a-9adb-197682150192
Hope it helps