So, I have an i5-2500k in an Asus Maximus IV Gene-z/GEN3 mobo. Whenever I overclock my CPU to 4.2ghz (the overclock is stable, tested it with intelburntest), the onboard adapters (LAN, audion, etc.) simply fail. When I boot into my overclock everything is working except my PC doesn't recognize the network adapter and I don't have sound... then when I reset everything back to normal sound comes back and so does the internet... I'm pretty sure I did everything right in the bios config and my overclock IS stable.
More aboutintegrated adapters disappear overclock
Did you mess with BCLK? Many system clocks are derived from it, overclocking BCLK may cause PCIe and other devices to mysteriously 'fail' and come back after overclock reset.