Q: I passed from Windows XP to Windows 7 and iTunes consider my computer as a new one. So it refuses access to my account saying that it makes more than 5 authorized PC's. Except for my laptop, all the previous authorized ones were mines that I replaced

I passed from Windows XP to Windows 7 and iTunes considers my PC as a new one. Each time I replaced a PC by a new one, I was unable to unauthorize it since it didn't word properly anymore. So, for iTunes I have reached the limit of 5 computers authorized but really, I just replaced them and they has always been mine (except for my laptop). I don't have access to my music anymore. I have bought quite a lot over the years and I am very frustrated about not being able to recover it. Any solution suggested to erase the previous computers authorizations?