Itunes crash on startup or when accessing the store

Question

Hi,
I upgraded to iTunes 12.0.1.26 from iTunes 11.1.1.11 on a win7 sp1 system.
When I start Itunes, it crashes after a few seconds "iTunes has stopped working...".
Log Name:      Application
Source:        Application Error
Date:          14/01/2015 05:46:13
Event ID:      1000
Task Category: (100)
Level:         Error
Faulting application name: iTunes.exe, version: 12.0.1.26, time stamp: 0x543e558b
Faulting module name: WebKit.dll, version: 7537.60.17.14, time stamp: 0x53da8e3b
I have since then uninstalled all iTunes ansd Apple related software as instructed in Troubleshooting issues with iTunes for Windows updates (uninstall, reboot, regclean, check for remnants and delete them, reboot, reinstall) without any luck.
Removing the iTunes preference files as instructed in iTunes for Windows Vista, Windows 7, or Windows 8: Fix unexpected quits or launch issues - Apple Support seemed to allow me to start the application but as soon I try to access the iTunes store or log in, the application crashes again.
I'm out of ideas.

Answer 1

Update:
after once more removing all installed Apple products I deleted all folders in c:\programm file (x86)\; c:\users\user\AppData\ etc. that had anything "Apple" or "iTunes" in them ( Apple, Apple Computer etc). Additionally, I renamed any iTunes folder I could find in my media folders.
So far, I was able to start iTunes 12 and sign in to the iTunes store. I de-authorised all computers and authorised the machine I am sitting at. No crashes yet.
Now I just need to read up on how to import the music, apps, books and movies I purchased a while back.