That sounds like a free trial copy of Microsoft Office that was good for 25 uses (of all Office programs combined) or 60 days. At the end of that time it stops letting you edit your files or create new ones. You have to purchase Microsoft Office 2010, or at least Word 2010, to do that.
Note: The 25-character product key on the computer case or laptop bottom is NOT the key for MS Office. It’s only for the Windows operating system.
Here are some of your options for legally paying less than full price for Microsoft Office 2010:
First, if you're a student, you may qualify for the Office 2010 Professional Academic edition at a pretty good price ($79.95):
http://www.microsoft.com/student/
Second, if you’re interested in buying just Word, check out this URL, especially the second group of listings.
http://office.microsoft.com/en-us/buy/office-2010-pricing-information-HA101810737.aspx
Also, if you have files that are locked up in the new Word 2010 file format (.docx), here’s a possibility for salvaging them. Microsoft offers a free Compatibility pack that allows earlier versions of Word (and Microsoft Works) to read and write Word 2010 files. If you have access to an earlier version, this can at least give you back your documents. Some new features of Word 2010 will be lost or converted to straight text in the conversion to the earlier version.
Good luck.