What Operating system are you running it on? Quite possibly it's not compatible, especially if you're running on a Mac with a recent OS.
Sorry to say, but you really can't afford not to upgrade. FMP 11 was the last of the fmp7 versions. All since then are fmp12.
As Vaughan said if you uses above 10.12 probably its not compatible. and FileMaker 11 support has ended at Sep 25, 2015 itself (Ref: FileMaker announces end of support for FileMaker 11 product family | FileMaker ).
But a chance is there for get your FileMaker 11 Back!
Go to this following link & fill-out your requirement & submit. Link : Contact us | FileMaker
Surely FileMaker Support team will respond quickly.
Reply to that mail with your current FM11 licensing details for verification as they asked!
That's it! After they verified, Will forward you the direct download link for FileMaker 11 licensed copy!
Install It! Enjoy!!
Hope It Helps,