WEBSITES ARE PINGING BUT SITES ARE NOT BROWSI

Hi
iam also faced same problem iam having duty on sunday all user's working fine till 3.30 suddendly after that my users
complain me that internet is not comming when i try to ping the website they are replying but iam unable to browse ,
when i contacted my isp he told me that from our side all things are fine but from u r side firewall is blocking
i have zero knowldege about firewall when i contacted my senior(he is on weekly off,and he know firewall well ) on phone he told me that firewal is not blocking , problem is from isp only, i spend 4 hours to get the sites but i failed , lastly i configured proxy server then i get internet , when my senior came on monday at 10.00 am, at 10.10am he told me that internet is comming , i did nothing he is saying,,,,, i want to know what might the problem, is he reset the firewall setting or problem from isp only
iam waiting for your reply



thanx


with regards
akbar