Default play store and facebook not working XPERIA M

hey guys...
im new to xperia m....
i have had plenty of experience with samsung phone though... u can see my threads...
problem is whenever i open playstore it says no connection... i cant even sign in my any account to phone... even facebook doesnt work... but other interned apps like whats browser etc worl fine... this ony happens on wifi... everything works perfectly on packet data !
it was working earlier... but from one day i have this problem... any help will be appretiated thank u
sorry for hopeless spellings
PLEEZ REPLY !!!!!!!!!