Why do apps only display in top left quarter of screen after installing Winterboard? After installing the jailbreak app "Winterboard" just now and then rebooting as required, all my apps including settings and phone etc. only display in top left quarter of screen. 

Only that screen quarter accepts touch input, but the touches are relative to the entire screen. This means I can't interact with the bottom and right halves of any apps, making it impossible to revert the installation.

Googling for this problem tells me that it was a problem with the version iOS 5 GM, which is a pre-release. But I'm not using that; I've just installed the newly released iOS 5.0.1. 

Also, the recommended fix is to use SBSettings to start in failsafe mode, but I never had SBSettings installed, and I can't install it now with the screen acting up this way. 

How can I fix this problem, apart from restoring from my PC?
I know I can restore from backup and then re-do all the jailbreaking, but it'd be nice if there was a way to avoid that.

This is what I've done:  


I first made a backup to my PC, then the iOS 5.0.1 upgrade, then a restore from the PC to make sure I had all the apps and data again (I didn't; somehow several apps were missing after the restore, but I just installed the rest manually). 
After that, I did the jailbreak and started adding Cydia apps. One app required the installation of Winterboard, and that is what caused this problem. 
I'm fairly sure Winterboard is the culprit because when it happened, I restored again, jailbroke again, and began reinstalling Cydia apps again in a different order. It broke like this again while installing a different Cydia app that also requires Winterboard.
There's a weird effect going on that indicates that although the size of the displayed image is reduced but the size of the touch area remains full-sized but unresponsive outside the displayed quarter of the screen. In a paint app, I can drag from inside the display quarter into outside, but I cannot start a touch outside the display quarter; nothing happens.


So I know that I can "fix" the problem by restoring from the PC again and avoiding any Cydia apps that require Winterboard. But I would like to avoid restoring if possible, to save myself the trouble. I'll keep that as a last option in case there's no other way to revert this.
Ok, according to this Cydia thread, you have installed an iPhone 3GS wallpaper on your iPhone 4. Since the iPhone 4 has four times the resolution of the iPhone 3GS the apps will only show up in the left quarter of the screen.
Here's the fix:

Go to Settings&gt;Wallpaper and choose any of the default wallpapers. Hopefully that will work.

And you don't need to restore. Winterboard makes no changes to the original OS files.

Since you can't press the Set button, you will need to restore and make sure that you avoid any apps that use Winterboard. Too bad!! I hope I've been helpful!