We need more information: What version of OS X were you running before updating to Yosemite and which version of Family Tree Maker are you using? I checked the Family Tree Maker web site and they say nothing about Yosemite.
However, I copied this from the Family Tree Maker forums:
Thank you for the information. Although Family Tree Maker is not currently compatible with Yosemite, our developers are working to make sure that it will be.
Thank you for your replies. None of the "buttons" on my FTM work. Since posting this, I've learned that many other FTM users are having the same issues, but that the software developer is working to make FTM compatible with Yosemite. Again, thanks for your replies..
The problem John is trying to reinstall software that's not compatible with Yosemite may make it impossible to reinstall. We found that out with Office 2008 with Lion. It wasn't until MS issued an update that the 2008 installer worked. Previously, it looked for Rosetta.