D-Link router - "A network cable is unplugged"

[stevenrw]

Hello everybody - I need some help please.
A buddy of mine has a D-Link router (not sure of the model no.). He can connect wirelessly but his desktop machine (XP SP2) is telling him he's no connection and there's a message in the notification area "A network cable is unplugged"
Of course, the cable isn't unplugged.
He's changed the cable and checked the connection physically, he's also tried disabling his firewall but to no avail.
So he's asked me to take a look for him.
I know, blind leading the blind I hear you say..., but I do have the advantage of access to all you good guys don't I? (grovel, grovel)
Anybody had this? I read somewhere that D-Link are odd in as much as they operate MAC filtering on wired connections as well as wireless, but I don't know how to check that, as I've never had a D-Link router.
Any pointers would be (as always) gratefully accepted.

[Rik]

First thing I'd do is to go into device manager and check that the computer's network card is working, Steven.

[stevenrw]

Thanks Rik - yes, he's done that. Apparently (and unbeknownst to me ) he took his pooter to a local shop, they had the bonnet up and could find no fault.
No probs with the ISP (Madasafish) 'cos he can connect wirelessly.
So its a router issue I think.

[Rik]

Sounds like it. Has he tried all four sockets?

[Glenn]

Is there another PC that can be connected to the router to test it?

Factory reset the router and start from scratch.