Which ver of Photoshop?
Did you restart your computer after updating Yosemite?
I can't even recall the version I had. I've had it for maybe 6 or 7 years.
yes, I did restart it.
Using 6-7 year old software that's no longer receiving updates & was never designed to run on 10.10 is asking for trouble. That said, try re-installing PS and installing Java SE6
It might work. But again it might not.