Unable to connect to network

HELP.

I've just installed a new modem as a result of upgrading by broadband and my windows 8 PC won't connect. I've googled and followed almost every tip

ipconfig /release
ipconfig / renew

ipconfig /release6
ipconfig / renew6

ipconfig /flushdns

plus whatever else is out there. Every other device worked a treat except my desktop on windows 8.

When I try and do a ipconfig /renew it goes away and eventually comes back saying it could not find the DHCP server, what am I missing???

help please