Yes it's Real Player Plus. Uninstall it and things should work. I just wish Apple had steered me to this instead of all the other wasted troubleshooting. I finally got soooo frustrated I did a clean install of WINDOWS! Then I installed iTunes first thing and as I reinstalled all my other programs (including antivirus etc) I then tried to access the iTunes Store and installing just Real Player did not do it but when I signed in and updated the Real Player, it downloaded more software (the Plus part) and then bam that was when the iTunes Store went white. I uninstalled Real Player and then it worked. Hope this helps others.
Now what to use to play all my videos with....Quicktime does not cut it and Media Player either.