apple id errors

Hi. Several times in this months my hackintosh change itself the serial number. When I start the macOS a message saying that can't connect to icloud appears. I verify my account and connects ok but when I check the serial is different and several imacs appears in the apple id page. Any ideas of...

I am able to sync my notes & calendars through iCloud and I have my Apple ID associated with my user account, but I cannot use iTunes or the App Store. When I try to buy/install an app from the App Store, I get small red text under my Apple ID that says "An unknown error has occurred". Clicking...