The company i work for just begun hosting a new website and had to transfer the domain name from the ISP to a different hosting company.
Now the website is accessible from outside the network but not accessible from inside the network. The ISP is the same and we can't access the website using our ISP. It doesn't resolve the DNS Name at all.
If i try to ping the website, it says "host lookup failed", even nslookup is failing. When trying to access the website via the IPaddress, it refuses.
The problem is in the ISP but I don't know how to solve it and our ISP isn't being very helpful.
This often happens when someone is running authoritative and recursive DNS on the same servers. Which is why you should never do that :)
It also happens when your local domain (Active Directory?) is the same as the domain you use at your hoster. Never do that. For example: if your domain is example.com then don't use example.com as your local domain. If you do then both your hoster and your own servers believe they are authoritative for that domain. Once the zone data starts to diverge you have this kind of weird problems. Instead use a subdomain of your domain name for your office, like office.example.com so that example.com can remain authoritative at the hoster.
If you do have the same domain both locally and at the hoster then you have to manually make sure that the information in your local DNS server stays in sync with the hoster's DNS server. For example: if your hoster has record www.example.com A 192.0.2.1 then you have to have the same record in your local DNS server. When the hoster changes the record to e.g. www.example.com A 192.0.2.222 then you have to make the same change otherwise your local DNS server will keep telling you that www.example.com is at 192.0.2.1. The same happens when you change hoster as they will almost certainly use different IP addresses.
So if you can then don't use the domain name itself in your office but use a subdomain. If that is impossible then you will have to manually keep the hoster's and your own DNS zone data in sync. Because this always goes wrong and breaks in 'interesting' ways really try to use a subdomain though!
PS: and never ever use somebody else's domain name as your local domain. I have seen ICT companies use local domains like <localcityname>.com and then suddenly the whole company can't access the real domain anymore because the local servers think it's theirs.