I recently upgraded the CPU in my DZ68BC motherboard from a i5-2500K to a an i7-3770. This had plenty of issues but they have been mostly resolved. The two remaining issues are related in operation, though I don't think they have anything to do with each other.
The first issue is that the system will not come out of sleep mode reliably. For short periods, sleep will work properly about half the time. On longer periods, upon waking up, the system will either sit there with no monitor activity, but appear to otherwise be booting up, or it will flash a blue screen with an error message and shut down. The resolution for this is to not use sleep mode and just shut the system down when it is not going to be used for an extended period of time.
The second problem is that on a fresh start up, frequently the ethernet communications do not work. An examination of the device manager shows a ! for the onboard NIC. The solution to this problem is to open the driver panel and disable, then re-enable the driver. This works every time, but it is a bit of a hassle to do each time you start the computer.
I've gone to Intel's support page and confirmed that all of my drivers are up to date. I have re-loaded the file Prowin188.8.131.52 at least twice. I've found a site that has the earlier versions of this driver. My question is: Would dropping back a few revisions on this driver be likely to resolve the problem?
The last version of the drivers are: 18.8.1 (2014-1-13). Did you already try those? (sometimes the DZ68BC download page doesn't list the latest drivers).
With Windows 7 I had also some issues in the past that the NIC wasn't correctly detected at startup. I am now on windows 8.1 and haven't seen that problem again.
You can try to disable some of the "power options" and wake up options. I had to disable "wake on pattern match" to prevent that my system wakes up to many times.
Windows 7 has also build in drivers, you can check if these work better. Most of the Intel driver "improvements" are mostly intended for server systems anyway.