I don't know what kinds of problems you've had in setting up a new computer, but I've had a bunch over the past few days. I already wrote about the iTunes problem. Well, since then,I've experienced a strange phenomenon: the PC would suddenly shut down, then start up, then shut down, repeating the cycle every few seconds, until I turned off the main power. When I turned on the power an hour or so later, it started up normally, then about 5 minutes later, it started the on - off cycle again. Not knowing anything better to do, I restored the system to Day One. That meant re-installing all my programs, and re-copying files from my external hard drive. This time I kept a log listing each step of progress. And I've been selective in copying files. So far, so good.
The problem with the duplicate iTunes music was overcome as follows:
I went into the external hard drive and deleted the complete music file. Then I copied the music file from my laptop into the ext. hard drive, then copied it into the new PC. Problem solved! It turned out that the ext. hard drive had been storing earlier versions of the music file, including some duplicate items.
It seems as though I almost know what I'm doing.