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Question: its about my canon 1000d eos kiss f

I have my secondhand eos 1000d kiss f canon this last two days ago and i found out that when i use the liveview the auto focus is not working even i ready set the function in auto focus. so what seems to be the problem with that? is it on my lens or in my cam itself? because i already change the lens but still the problem is there. please reply @ mcj0031@yahoo.com