[Craig Alan]"Did perhaps the install of CS5 replace the proper version of QT that FC likes"
It cant do that. Apple would never let a 3rd party software change QT witch is core to the mac OS like that.
As for the question, im going to respond to that on your original question post. Double posting, especially multiple times a day makes it HARD for others following to know what others have suggested, what you have tried etc.
Often when double posting you just get different people suggesting you try the same things that you were suggested in your ordinal post.
I've had this problem in the past.
Try going into your System Preferences and change the resolution of your monitor(s) to some resolution lower than what you normally have it set at. See if it helps the white screen problem when you launch FCP. After I changed the resolution, it worked fine. After I changed it back to normal, it still continued to work.
Also try creating a new user and open FCP logged in as the new user. That's worked for some.