White screen in Xcode 4.2 after conversion to Objective C ARC - xcode

Question

I have combed through the entire internet looking for this answer , and have found nothing, so I have decided to post.
EQUIPMENT: Mac Mini (2011) , running OSXLion (10.7) , 8gb ram, 500gb hd
XCODE: version 4.2, running IPAD 4.3 and 5.0 simulators
I have developed an Ipad app using the program HYPE (html 5 designer/generator), this program was developed by an APPLE team. I then brought it into Xcode using the PhoneGap template. I had developed this app in a previous version of Xcode (4.0 using MAC osx snow leopard) and was able to transfer everything into Xcode 4.2 (including the phonegap template) successfully.
All was running fine. I launched my app in the app store successfully (Five Element Clinic Book HD - http://itunes.apple.com/us/app/five-element-clinic-book-hd/id495512918?alreadyRedirected=1&ign-mpt=uo%3D2&mt=8)
I noticed some issues I wanted to change (namely the external hosting was not working - my embeded youtube video (iframe) was not working, links to external websites not working and an iframe bringing in a counter script (javascript) also not showing - so I decided to take a look at everything to see if I adding more detailed URLs in the phonegap.plist external hosts area would work.
I didn't even get that far. When I opened Xcode again (after about 2 weeks, so there must have been some kind of API change) - I had a tone of errors that lead me to the information of needing to Convert my files over to Objective C ARC.
So I did this, with no errors or issues. Everything converted seamlessly. All files are showing converted to Objective C ARC.
I CLEANED then reBUILT - with absolutely no errors or warnings - and RAN my app in the IPAD simulator (4.3 and 5.0).
This is what happens. The simulator opens, my app launches, the start up screen shows, the app begins to load the rest of the app and just goes to a WHITE SCREEN. Forever. It goes no where else.
So I have quit the app, restarted the app, deleted the app, tried everything again. Same issue. If I quit the app it just goes to a black screen. I have also restarted Xcode and my computer, ran my disk warriors to fix file permissions, etc.
I still have my old project in my old laptop (Xcode 4.0, MAC OSx Snow Leopard). So I went back there to see if I could just work from the old environment. Nope. Same errors that require me to convert files to Objective C ARC. So I converted with zero issues and zero errors. Cleaned, Built - no errors) and ran the program in the simulators. None of them work, everything loads the start-up screen and goes to a white page.
Does ANYONE know what is going on?
And thank you.

Answer 1

Mine was not a white screen - but a black screen.
In applicationDidFinishLaunching I was using the result of
UIWindow* window = [[UIWindow alloc] initWithFrame:mainBounds];
as a local variable.
Converting to ARC released it.
Instead it needed to be assigned to a property of my app delegate:
#interface MyAppDelegate : NSObject <UIApplicationDelegate> {
UIWindow *mainWindow;
}