Hi Jack,
OK, try the following:
1. Click on Office Button|Word Options|Add-Ins > Manage > Disabled Items > Go.
2. If Building Blocks.dotx is listed, click it, and then click Enable.
3. Exit and restart Word.
If Building Blocks.dotx is not listed, the Building Blocks.dotx file may be enabled but damaged or missing. In that case, see:
http://support.microsoft.com/kb/933312