Why doesn't iTunes recognize authorized computers?

Thank you for the reply. I am not prevented from playing purchased items, only challenged every time I make a new purchase to go through authorization steps. I've had iTunes installed since it was first available for Windows and am on my 5th or 6th computer that's been authorized. Yes, I deauthorize retiring units. Yes, I've sync'ed units. At present, I have it authorized on 3 different versions of Windows. It's only been a problem on the newest notebook which is less than a year old and running Windows 7. All units are kept up-to-date with patches and versions of everything that's installed. The problem with iTunes authorization began this summer within the last few iTunes updates. I also had an anomaly right after rebooting following one iTunes update where the program came up playing a song even though it was not opened by me. I had to kill the process in the Task Manager to stop it. I rebooted, and this did not happen again. I don't have any questionable software installed, only commercial apps for typical business and hobby functions, nothing that should cause iTunes to go rogue.