LAN issues on my desktop PC

Hello,

So, here is the situation:

1. I bought a new desktop about 20 days ago. It’s running an ASUS M5A97 R2.

2. The machine arrived with Windows 8.1 already installed along with all the drivers.

3. I plug in the LAN cable—nothing. It is as if nothing is even plugged in; there isn't even a flicker from the LED on the modem or the port on the motherboard.

4. I take that same LAN cable and plug it into my laptop—everything works perfectly fine via Ethernet.

5. Thinking the LAN port on the motherboard was dead, I sent it back to the service center. They tested it with a cable, and it worked fine for them. Then they sent it back to me.

6. I get it home, plug the cable in, and... still nothing.

7. I use the same cable on the laptop, and it works.

8. I tried connecting the desktop through the laptop using a different LAN cable while the laptop stayed on Wi-Fi, and—suddenly—the desktop has LAN access. So, I assumed it was just a bad cable.

9. I move the desktop right next to the modem and connect it directly using that second cable—still nothing. So, it isn't the cable. Again, no LED lights on either the modem or the motherboard.

10. I called Comcast, and they tried resetting everything to factory settings, but it didn't help. They didn't have much else to offer, mostly just throwing out excuses like "you need drivers" or "your motherboard is faulty."

11. I have checked the drivers about ten times now. Everything looks perfect, no errors reported (which makes sense, since they checked them fifty times at the service center before shipping it back today).

The desktop settings are all on default (automatic IP/DNS); I haven't touched anything.

Does anyone have a clue what is going on? For some reason, a signal just won't establish between the desktop and the modem. When I bridge the connection through the laptop, the desktop recognizes the modem and connects to the LAN. I have tested this on both Windows 7 and Windows 8.1. I've already disabled any power-saving options that might shut down the LAN, and I tried turning off Green Ethernet and Energy Efficient Ethernet in the network settings, since I read those can cause issues, but no luck.

The modem is a Thompson TG782i (I know it's garbage, but it's what Comcast provided), and the controller is a Realtek PCIe GBE Family controller.

The drivers are the latest versions and everything seems fine; Device Manager shows no errors.

Thanks in advance,

silvermoose14

It looks like you’ve pretty much exhausted every single option available—from swapping out the second LAN cable to messing around with those drivers. At this point, you might as well just call Comcast and demand they swap out your router entirely, or maybe just grab a USB Wi-Fi adapter and bypass the whole mess by connecting that way. Honestly? I'm running out of ideas for you...

So, I just took it over to my cousin's place. I hooked it up to his modem using that same cable, and it worked instantly—it recognized the connection, grabbed the signal, and jumped right onto the LAN.

Is it even possible that it won't connect at home because of some stupid little glitch? Like, maybe since my laptop and desktop have the exact same name, the network isn't picking up this one as a new device?

Anyway, I’m probably just going to ask for a new modem. That should fix everything, I guess.

So, you’re telling me you hooked your PC directly to your laptop using a LAN cable and the connection works perfectly fine, yet when you plug that very same cable into your modem, absolutely nothing happens? If we follow the breadcrumbs of logic here, there is really only one reasonable conclusion: you’re likely holding an Ethernet crossover cable, and that stubborn modem simply refuses to recognize it. What you actually need is a standard Ethernet straight-through cable to establish a connection with the modem.

http://www.computer-hardware-explain...ver-cables.jpg

Take a look at this image. Check both ends of your cable—are the orange and green wires lined up in the exact same order on both sides, or are they flipped? Once you verify that, you'll know exactly what kind of cable you're dealing with.

...That’s what you'd think, though, since he claimed everything else was battle-tested. It's just that nowadays, network cards don't care if you're using a crossover cable or not.

Look, I realize how bizarre it sounds, but honestly, isn't it better to be safe than sorry? It certainly wouldn't hurt to double-check everything just in case.

Problem solved

Just as I suspected (since I’d already ruled out everything else), swapping out the modem did the trick. Everything is running perfectly now without any errors.

The old modem just wouldn't talk to my desktop, or maybe the desktop wouldn't talk to the modem. One of the two.