Unable to acess website in intranetwork

Dear Friends

I m working for 1mnc as sys-admin we are facing problem in acessing 1website in our intranetwork but if we try to acess site using IP address provided by our ISP its works its not working in our internal network and gives result as page under construction and if we Ping “Website Name” it pings ipadd address of our DNS server not websites ipaddress.

I found that relevant ‘A’ record is added in DNS how do i resolve this and external webaddress has same name as intenal

I m not able get whats problem

pls help