i can't access itunes, appstore, even the website www.apple.com using my wifi i can't access itunes, appstore, even the website www.apple.com using my wifi, both on my iphone or pc. 
i've tried to looking for the troubleshoot problems using my windows pc and it says
"Windows can’t find the host name "apple.com" using DNS" what should i do?
It doesn't look like Apple specific question. It looks more like network setup question. You need to check your router settings. Looks like you have either wrong or missing DNS addresses. If you don't know what it is, call tech support of your internet provider.