Plugged it back in to what turned out to be a different port on the router and went on with using the PC.
Later on I went to get a drink and on coming back I noticed an LED on the motherboard of the machine (which has a side window and unused fan grills on the top of the case) which was usually green had turned Orange.
I reached for the motherboard manual (it's a Gigabyte H61MA-D2V) to find out what the light meant in case it was some kind of diagnostic indicator.
Absolutely no detail in there.
Rebooted and the machine passed POST and loaded windows 7 as usual, light still orange so I left it and went to bed
Came back today and again still an Orange light, determined it was an Ethernet link light by disconnecting the cable and the light went out, by a process of elimination it appears that, like on routers the colour indicates the link speed (Orange = 1 Gbps Green = 10/100 Mbps)
To cut a long story short I tried all four Ethernet ports on the router (and no it wasn't plugged into the EWAN port) and all connected at 1 Gbps apart from port 3.
Its running the latest firmware and I reset it to factory defaults, but this did not fix the issue, anyone else had a similar issue with this device?
Router: Billion 7800N
Note: I don't lay turf for anyone. astro or otherwise, all views and opinions expressed are my own based on experience.