Need help accessing a website

I have a Laptop an iPhone and a "vintage" iMac on OS 10.6.8, all connected through the same hub, when trying to access my website "www.psychoontyres.co.uk" the G4 laptop and 3GS phone have no problem getting through but the i-mac in Safari 5.1.10 comes up "Can't find Server" and Firefox 40.0.3 says "Server not found".

I have no problems accessing any other website on my i-mac, any suggestions for a fix would be most welcome.

If you need any other information please fire away.

Thanks