First, you didn't tell us whether Word 2007 was installed on your computer.. If it's not installed and activated, then you'll need to install the program, or at least install the Word Viewer from the link below:

http://www.microsoft.com/downloads/en/details.aspx?FamilyID=3657ce88-7cfa-457a-9aec-f4f827f20cac

On the other hand, if you're sure that Windows 2007 is installed, then opening a Word file should automatically open the file.. If it doesn't, then you may have malware, or the association has been damaged somehow.

To reassociate the file extension to Word 2007, follow the instructions below:

http://www.techrepublic.com/article/how-do-i-change-file-extension-associations-in-windows-vista/6172036

And if malware has caused the problem, try downloading, installing, updating, then running a full system scan with the free malware removal tool below:

Malwarebytes Antimalware

Hope this helps.

Grif