Trouble connecting

Im out of ideas

So I bought a new computer recently and decided to give my old computer to my youngest brother for his birthday, as it was-is still a pretty decent comp.
After getting all my old files off. and uninstalling some programs I didnt think My lil brother needed to be playing with (Dragon Age, ect), and checking that everything still checks out ok I send my comp to my parents and get it set up.

Tried hooking the computer up wirelessly, no surprise it didnt work. I had issues with wireless when I lived there 2 years ago. That house just eats up wireless signals :|

So dad finally gets around to running a wire from the modem all the way across the house to the computer... and it wont connect. They call me over, and I fuss and fiddle with it... and I get it to recognize that it's connected to a modem, but not the internet.

Frustrated I take it home with me and connect it to my internet where it does the same thing. A week ago it worked just fine. I've tried everything I can think of. All things seem fine, drivers appear to be working, the wire is new and works on my bro's old comp. Tried diabling and reenabling the drivers. Teh network devieses. Rebooting the comp (Stupid but eh..). Made sure the network card hadnt somehow gotten disconeected from the motherboard. Disabled firewalls, virus protection, adaware, ect.

I'm completely stumped. The only other option I can think of is that the network card somehow got fried between the last time I connected on it and the first time I tried to connect at my parents.

Anyone have any suggestions?
The comp is about 4 years old.
Is win XP

Edit:
On a slightly unrelated note. Does anyone happen to know for a fact if BestBuy thinks Firefox is bad?
My dad and I got into a fight over whether it was the cause of it all, because he thinks Firefox is the devils work, and has been told so by the folks at Best Buy. I personally think he's lying.

Dunno why BestBuy would say anything about Firefox lest their employees are avid fanboys of other browsers. Ultimately, you can't go wrong with any browser tbh.

Just to check, when you say you're connecting to a modem, are you the only person trying to connect to it? Otherwise if you have multiple computers your modem would need to run through a router as well as a switch, with the computers of your network converging via the switch.

If you are running through a router/switch, have you added your computer's details (Such as its mac address) to the router and supplied it with an internal IP? If not, it won't be able to route to your computer.

Have you taken the laptop to somewhere like McD's or some place with free open wireless to see if it connects? That's a good starting point to see if it's the laptop or just some settings that need fixing.

As for Firefox, I religiously used IE for a long time and was very against even trying FF. I'm glad I did and I'll never go back to IE. Pages load faster, there's nothing bogging it down like all of IE's junk, and it's pretty well compatible to everything on the web, and it's also the most popular web browser (you can find the stats all over the web). There was an article published last year stating that it's even more secure overall than any other browser out there currently.

So yeah, I'm all for FireFox. :D

I don't suppose someone tried shoving an RJ-11 ("phone") plug into the ethernet socket between the time that the ethernet nic last worked and now...

The RJ-45 ("ethernet") plug is a bit wider and has four extra contacts. You can clip an RJ-11 plug into an RJ-45 socket, but you'll end up bending the two outermost pins on each side of the socket -- those pins carry data.

Does the modem/router show a 'green' DSL light? (I'm assuming your trying to connect via ADSL).

What model is the modem/router?

Use ipconfig inside a cmd prompt, are you being assigned the correct IP that the router/modem should be generating? (For example Netgear routers start 192.168.0.*)

Can you ping the router?

I'm not sure what light is on. I do know the other computers in the house were able to connect, however.
Im not forsure if they use dsl or cable now. They keep fliping between the two, mostly because the wireing is the same wireing my great-grandpa used when he built the house and it doesnt seem to take well to modern technology XD.
IIRC the modem is a belkin.
I'll check tomorrow and see if I can ping it. No time today :|

Im fairly certain that dad didnt try to plug a phone cord into the ethernet plug, mostly due to the above mentioned wiring problems wont let them have a regular phone (that works reliably). I wont rule out the possiblity my lil bro didnt find an old cord tho.
Both swear they didnt change a thing on that comp.

Thanks for the advice so far guys!

O_o

I think now is a good time to describe your network topology:

(choose one in each of the bracketed choices, or replace with a more appropriate answer)

* Internet comes in over: [a phone line + dsl; coax + cable; a phone line + dial-up]

* The [phone line, coax] plugs into a [modem and the modem is connected to a router; modem+router combination box]

* The working computers connect to the router using (choose all that apply) [wifi; ethernet over unshielded twisted pair cable; through some bridge device, like a HomePNA adapter]

* The non-working computer connects to the router using [wifi; ethernet over unshielded twisted pair cable; through some bridge device, like a HomePNA adapter]

Heh The internet comes in (as I said not sure anymore if they're useing dsl or cable)
It plugs into a modem

Said modem is/can also act as a router. As in - there is not a second peice of equipment before going to the computers.

Of the 4 computers only 1 is wifi (Dad's netbook). The others (including the problem) are hard wired. I.E. Use Ethernet.

Given the distance between computers and modem, two (not counting dad's) of them should be wifi. But something about the house/area eats the signal. Even adding a more powerful wireless router makes it sketchy at best.

Ah, thanks.

That helps a bit. The router+modem thing should have a link light for the port plugged in to the problem computer. The link light is an LED that lights when the port senses an ethernet signal, and may be located on the back integrated into the port, or nearby, possibly on the front. Make sure the link light goes on when you plug in the cable to the computer (and goes out when you unplug it).

The computer should have a similar port with a link light. If you can't find the link light, windows should tell you the connection status when you double click the network connection in the control panel (network connections item). The link light, if present, should go on with the network cable plugged in and off when unplugged. If no link light can be found, the connection status should toggle between connected and media disconnected.

Both sides need to reflect physical connectivity before going further.

The link light was showing up on the back of the computer.
And the computer was saying connected.
I never thought to look at the link light on the modem.

I do know that when I unhooked the problem computer and hooked up his older comp it all worked flawlessly.

I'll check that later today when I go over there.