I had gotten error "523" with a white screen and when I could get my phone to load all I would get is just a blank screen with only my background showing (no icons or menue options available). So it sounds similar to your issue
Can't promise that this will work but I would connect your phone to the desktop software on your computer. I would then delete that zombie app that you said was where the problem started. Then take out the battery for a minute or so and reinsert it. See if that resolves the issue. If it does, then you are good to go.
If it doesn't, then I'd back up the rest of your data. Then I would do a firmware reinstall from the desktop software. Go to the desktop software & to where it says check for updates in the drop down menue top left. It should check for firmware updates. And either update to latest available firmware or say none is available. If it says none available, then select where it says "see available firmware" & select the most recent available. It may tell you that you already have it installed & ask if you want to reinstall it, & you then say yes. Process may take about an hour.
I found that this helped me as I don't get any errors anymore & it also restored all of my icons. Turned out in my case the issue was something in the backed up data I had so unfortunately I don't have my backed up data yet. But at least my phone works perfectly now. In your case it may just be the Zombie app since you indicated the issue started when installed that app. Hope this helps.
