Welcome to the forums Steve! Sorry for your troubles [:s]
Please see my signature line for instructions on Logging. I would be good to see logs.
Does the app start and then shut down before really opening, does the dock icon bounce, or does NOTHING happen? Do you know when Logos updated last?
Side note: Make sure you type a message in the thread body, and not just in the subject line!
Mine seems to be working ok after an update to 10.11.4 Beta (15E64a) on the iMac and 10.11.3 on a macbook.
So I think those logs will be needed to sort out your particular problem.
