internet working on Static IP but not DHCP

I have a few machines on DHCP who can't access the internet. If I give them a static IP then they work ok. The DHCP is correctly configured and the results from IPCONFIG /all are exactly what I expect and pretty much the same as the static IP's except they are they DHCP range. The machines with DHCP can access everything internally on the network and WAN but not the outside world like WWW. or Skype. The machines are resolving DNS, so this is not the issue. There are no IP conflicts either.

Any advice on what could be causing this would be great.

Thanks

Martyn