To isekii,
As someone with a small network and as someone that used to experience those little " a network cable is unplugged" popups off the taskbar, it seems to me that you are in trouble shooting mode now.
But the following thoughts strike me now.
1. On the face of it, as you over clock the system and the bus, everything, including your Nic has to speed up. To test, go back to standard speed and see if the problem goes away. You can also play around with the NIC settings and drivers. It will also give you a clue if your cable is defective in some way. Also try wiggling the cable connections at both the ends while the network is running and see if that triggers a crash. Which would tell you the cable is defective. Since I assume you know your over clock bios settings, you can also go back to your otherwise stable over clock easily.
2. The fact that you have to physically replug the cable to get the network back screams at me. I immediately get the idea that the NIC broke your network because it lost its addresses which are likely dynamically assigned. And when I experienced the same problem with what was almost certainly an intermittent NIC, I solved that problem by assigning network addresses statically. It did not fix the intermittent NIC which otherwise only screwed up like once a day or so, but the pop up network cable is unplugged would almost instantly be followed by a popup saying the network cable was replugged. Changing what was a major hassle completely re set up the network into a minor annoyance that required no human intervention and only lasted a second or so. Because everything knew the static address it was supposed to have,
its able to work past the brief disruption and with a dynamic address its totally confounded until something tells it to assign new dynamic addresses.
3. You are going to get another NIC, after all, its very hard to hardware fix the on board NIC without replacing the mobo. Does the new NIC fix the problem? If not, you barked up the wrong tree, and its somewhere else. Maybe in your router or some other NIC on the network.
4. Most ethernet NIC's are capable of 100 Mb/sec transfer rate. I doubt your broadband even comes close to the speed.
So I doubt the over clock is responsible but its still a testable hypothesis.