My iTunes store is loading extremely slow - any idea what may be causing this?

I have a PC running Windows Vista with 3 user accounts on it. All 3 accounts have administrator privileges without restrictions. One of the accounts has absolutely no problems loading iTunes Store in a few seconds, but the other two accounts require you to walk away as it can take more than 10-15 minutes before the iTunes Store is ready to be used. Once ready those two accounts tend to time out for purchases because the transactions take so long. Does anybody have any ideas why?|||GET WINDOWS M0THERFUCKING 7