Problem with grayed-out Sort in Table

Hello,
I recently upgraded my computer operating system from Windows XP to 7. I had created a Table in Microsoft Word , but have now switched to LibreOffice and have saved the Table in Open Document Text format. I frequently add entries and depend on the Sort feature to rearrange them. When I just tried to select Sort from the menu in LibreOffice, it is grayed out and therefore not accessible. What do I need to do to get that feature back? Thanks.

I have made a little progress on this since I posted my question earlier today, but still would welcome some help. My table has 3 columns, with all the information in each row pertaining to a single item – ie, all 3 columns of data in a particular row need to stay together. I go into the table, place the cursor in the first column, go into the Table menu, and Select that column. Then I go back into the Table menu, select Sort (which is no longer grayed out), and I wind up with a table that has the entries in the 1st column sorted the way I want, but it doesn’t bring along the corresponding data in the other 2 columns. So I wind up with mis-matched rows. In MS Word, if you clicked on column 1 and selected Sort, it sorted by that column, but also knew enough to bring along all the corresponding data in the other 2 columns. How can I accomplish that in the LibreOffice Table function? I’ve tried all sorts of combinations of options, but nothing works. Thanks again in advance for any and all help.