iTunes store on Mac

I have been using iTunes for music purchases for years, but all of a sudden iTunes open but white screen with no content. I am signed in to the cloud, but when I try to sign in on the iTunes screen the id and password just disappears after entered and I go to login again and log in is still showing. I did manage to log in once via the iTunes page after I signed out of the cloud in system preferences. I spoke to apple a couple of days ago and said the security update should fix it. (high Sierra) it did for a day and now back to square one. very annoying. Not going to purchasing any music soon!