I can't access Facebook and Twitter on my home wifi?

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My problem is that suddenly, I can't access Facebook and Twitter apps on my IPad and cellphone. It says check the wifi connection again. But of course, my home wifi works fine. I'm still able to use Facebook and Twitter on my laptop (same home wifi), and use other apps (Foursquare, Instagram...) normally on IPad and cellphone. However, I can use Facebook and twitter app by 3G.

I tried to uninstall and reinstall both apps. But it doesn't work. My Mom's Ipad and cellphone have the same problem (cannot use 2 apps via home wifi, can only access by 3G). I think the cause is from Wifi. I unplug and plug again my wifi and modem. Nothing helped either. Please help me.