Update problems from 10.7.5 upwards

Hi, i have an Imac 27inch, Mid 2011.
processor: 3.4 GHz intel core i7

memory: 8GB

Storage: 2TB

Currently on operating system Mac OS x Lion 10.7.5.

i have a big issue from where when i try to do a software update it says "software update can't check for updates because of a network problem. software update can't connect to update server."

i do not understand this as my internet connection is faultless and works perfectly and i can use the internet on my imac.

So i cannot do an update from 10.7.5 and also the app store says "cannot connect to app store" im guessing these two problems must be linked.

i have tried doing it over wired connection, wireless stil no luck.

if anyone can help me solve this i'll be eternally grateful.

thanks, abu.