Will I hurt my credit by canceling my best buy card and opening a circuit city credit line?
I recently opened a best buy card to purchase a c.d. player, but two days later I found the same c.d. player for 400.00 cheaper at circuit city. It has not been 30 day since I opened the card and I haven’t charged anything to it. Will I hurt my credit by canceling my best buy card and opening a circuit city credit line?

Why close out the account for that? Just show Best Buy the ad from Circuit City and they’ll charge you that price.
Yes any new credit affects your FICA score for apprx 1 year after opening. Best Buy will usually match Circuit City’s price within 30 days of purchase.