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For the first few hours after having powered up the PC, the (Gigabit) network adapter is working OK. But by midday it starts to repeatedly disconnect / reconnect from the network. I can physically see the light on the switch flick off/on. Whilst surfing the internet it is not too noticeable - just a moments delay - but an alert pops up in the system tray that a network cable has been unplugged and then a moment later I get another popup saying it has connected. It is then only a few minutes (sometimes shorter) before it disconnects / reconnects again. As you might imagine, this is painful on the LAN.

When connected there are are no errors and all works OK. It's either on or off.

I have tried different cables and reseating the PCI network card, but the problem returned a few hours later.

The 10/100 built-in network adapter works OK, so it would certainly seem to be something to do with the network card or connection with the motherboard?

The network card is over 2 years old.

So, my question... is this a symptom of a failing network card? Or possibly something more serious with the motherboard?! Or should I just have another go at sticking the card in the machine?

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What connection speed do you have Gigabit Ethernet or just Fast Ethernet (100MBit)? – Robert Jul 26 '12 at 11:13
It's a PCI Gigabit Ethernet card connected to a gigabit switch with other gigabit devices. The built-in (motherboard) NIC that I'm now using is, however, just Fast Ethernet (100MBit). – w3dk Jul 26 '12 at 13:36

first of all try updating the drivers, I had a similiar issue with a PCI-Express Gbit NIC and updating the driver resolved the issue.

If this does not help you could still try the NIC in a different machine, against a different network switch/hub and different cables (I think you did that already).

On the other hand while a gbit nic sells for around 6 euros, you could simply buy a new one if the easy things don't work?

If you need some instructions on updating the driver you can have a look at this:

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