Hmnnn, probably you had a free edition of office suite application installed on your computer which will be valid for only 60 days. If you wish to continue using all the application of office suite, you will have to purchase the full version of office suite.
-See the following link for the price comparison:
If you wish to continue using the free trial version again, you will have to install different version of office trial suite again.
If you had Office 2010 Home and Student trial edition
installed on the computer before and it is expired, you can uninstall it and install the Office 2010 Professional trial edition on the computer which will be valid for another 60 days.
However, you also have the option of using the open office suite which is absolutely free. The open office suite provides all the features and functionality of the Microsoft application.
You can download the open office suite for free from the following link: