MBA wifi issues

Hi, my mba is the 2012 model, running OS X Mountain Lion10.8.4, I have this wifi issues since the previous version of Mountain Lion

The thing is my macbook cannot access to the internet although it is shown to be connected to the wireless router, my other device like ipad and iphone still be able to surf the web just fine while connecting to the wifi, my flatmate who use a PC never got this issue. And when I go to Safari, the web page just simply not loading instead of popping up the notice "you are not connected to the internet" as i turn off my wifi

This can go on for hours until I can access to the internet again, and this can happen many times a day.

I tried rebooting my MBA, and turn off/on my wifi but it wont work, the only thing that usually worked is reboot my router.

My router is Netgear dg834g running firmware v.3.01.38, I'm not sure if this is the problem with my router or my mac

Please help!

P.S: the wireless diagnostics didnt help much.