There could be 2 things that are wrong.
1) You have reached the end of the Microsoft Office 2007 Trial.
When this happens you are not able to edit any documents. You will only be able to view and print your documents.
To fix this you need to buy an office 2007 license from
http://office.microsoft.com
2) You are trying to edit a protected document.
Some people protect their documents or parts of their documents from being edited. The only way around this is to get an original copy of the file or the password for the file.try to recover the word password with word password recovery 5.0, which is considered as the best word password recovery tool on the market.
Hope this helps you!