Try these steps ClickHere
To remove the Office Professional 2010 trial included with installations of Office Home and Student 2010 or Office Home and Business 2010, follow these steps:
Open an Office application, such as Word.
Click the File tab.
Under Trial Product, find Microsoft Office Professional 2010 and then click Licensing Options.
Click Remove Trial.
Or you could use the 'fix it' utility ClickHere
After you remove the Office suite, you may attempt to reinstall Office 2007. Reinstall Office 2007 ClickHere Please read through all the links before you decide on your course of action. The last link is good as it has screenshots.
Word 2010 and Word 2007 are both .docx so you should be able to open them ok.