First you need to find out if it is the router or the NIC that is causing the problems.
Bypass the router and plug your computer directly into your DSL or Cable modem. If your computer makes a connection then you will know there is a problem with the router.

If it is the router it might just be a bad port in which case you can try another port on the router. Access the routers web interface and verify DHCP is running for the LAN.

If it's your NIC card you can try updating drivers or just buy a new one.

There was no need to disable the wireless adapter.
Post ipconfig /all with the wireless adapter activated, then with the wired connection.

Hey hughv, so can you englighten me on something then please: Is there or isn't there a consequence of having both a wired and wireless connection enabled on a computer, to the same network?

I'll post ipconfig /all details once I regain access to the PC, that's why I haven't replied all this while.

simple put your NIC is fried. thats the worst. if not here are a few thing, if you get a 169 Ip address it can be fixed, but if the fix resort back to the 169 then the card is definitely fried. is this card on board or PCI.
no consequence of having a wireless and wired connection. the point of this is that you can bridge the connections.(make them as one)

Bobbyraw is correct. It's quite common to have both connections enabled.

I'm not so sure now you know. To explain let me give a little bit more background information.

The computer was recently added to an office server domain. The users are added as "ordinary" users. When I started the thread, it was because as I said, when both the ethernet cable and the NIC were enabled and physically connected to the computer, the icon for the wireless connection would show that it was connected to the internet, but the icon for the ethernet connection would show that it was "acquiring network address".

Now as I mentioned in another earlier post, I left it for a while, and only went back to try it out yesterday. When I did this, It was to log in as another (ordinary) user. Then a new problem was discovered. Note that at this point the ethernet cable had been disconnected, the wireless card still of course left in, and enabled. When the user tried to connect to the network/internet, it connects, then disconnects, then reconnects withing the space of ten seconds, and keeps doing this. On the back of the tower, the green and amber lights in the back of the card are off one second, on the next, and so on. So drawing from that behaviour, one could say that the card was dodgy. This however does not seem to be the case, as when I log in as the administrator to the computer, the connectivity is FINE!

And the most recent update is, as of today, the user was still having problems when they were logged in with it cutting out and reconnecting erratically, so I sought to recreate the original problem i.e. have both wired and wireless connections, and when I do this, I get the same thing that happened before, wireless works fine, wired stuck on "acquiring network address". Needless to say I didn't try to see what would happen if I disabled the network adapter because the user had to get on with some work!

I know that I've gone on quite a bit, but it's only so that ppl can hopefully fully understand the behaviour. So whilst it could be a busted wireless card (connected through a PCI slot by the way) sometimes, at other times it seems like it's the ethernet cable that has a problem.

Would love to hear more options now, I can confirm that the ethernet cable worked fine on a different computer so I don't think that's the problem. Are there any more steps I can take to try to isolate the cause?

OK, I didn't want to open a new thread because the problem is related to this one, but there's a new but possible related issue.

I was working through a server domain before, but I decided to just log on to the computer's domain instead. Now before I log on, a wireless PCI Card is enabled, but there is no ethernet cable plugged in. When I log in, the wireless connection rightly says "connected", but I can't browse the 'net. I try to see what network it's connecting to, and it shows that message about WZC not being on and windows not being able to configure the network. I click 'advanced settings', and see that there is no 'Wireless Networks' tab. So I run services.msc, and see that WZC is indeed not running. So I start it, and then try to connect using Windows, and it connects fine, and I can browse fine.

Why was WZC not started automatically? It's a Belkin Network Adapter and it does come with a utility, but it's not used.

Your thoughts are appreciated.

Update: When I log off and log back on, WZC stays running. However when I restart I have to start WZC manually, even though the Startup Type is set to automatic...

Weird.
Maybe a driver update for the Belkin?
Would love to see ipconfig /all