Hi Sylvia
Sorry for the delay but we have been troubleshooting the system and while the results were good, wanted to wait and see if it stayed that way before I posted.
As I said, before I went inside the system at the end of June it was running stable and as I had not been removing or installing components, I knew that no screws or foreign objects could have been dropped inside the case that could be contacting components and causing a grounding issue like you suggested.
Therefore I focused my troubleshooting efforts with the system assembled inside the case.
What prompted me to do the following is that we actually started getting blue screens followed by automatic restarts, and my experience is that these are usually caused by failing hardware or occasionally O/S or program corruption.
I started by replacing the power supply with a known good spare, which had no effect. This was good because the normal PSU is the 1200 Watt Antec which is a very good PSU and should not be failing, especially since we also run the system of a UPS.
Logically I could not see why any other component should be causing BSOD, except that we had never been 100% confident in the stability of the video card. When I removed this and started running with the on-board HDMI the system started running a lot better, running smoother and more responsively. For example a half second delay after you clicked the x button to close IE or some other applications (an intermittent behaviour) disappeared and now this feels instantaneous as it should be.
So the freezing had disappeared after this. I did get one shutdown freeze where the progress circle/wheel in Win 7 stopped turning as it was shutting down, and with video editing in Nero we still had a BSOD after a half hour or so, but it was already a lot better.
The shutdown freeze and blue screening prompted me to do the following software cleanup.
1. System Restore to one week prior to removing video card, to refresh system files.
2. Uninstall video card driver software and Intel video, Intel Audio, Intel Networking and Intel Chipset software.
3. Install Intel Chipset software and then latest Intel video, audio and networking software.
End result to date (since above three steps done Friday 19th July):
* Mouse movement and scrolling of documents and web pages feels smooth again.
* No more system freezes or shutdown freezes.
* On several evenings system has been used for video editing in Nero 12 Video up to 2 or 3 hours at a time and a couple of nights ago we got 1 BSOD after over 2 hours of editing.
I still believe the BSOD should not happen and that software should produce normal Windows GUI errors so I am suspecting there could still be an O/S issue that the video card has caused over time and that it may be necessary to reinstall Windows.
As the system is sometimes used for video intensive tasks I will be sourcing another high end graphics adaptor to install into the system, and putting back in the Antec PSU which has the wattage to drive it properly, but can say that we are surprised at how well the on-board video on these Intel mainboards manages with these kind of tasks.
If Engineering can still release a BIOS that addresses the stability issues in the 3x BIOS versions that users have complained about in these forums and the other issues such as UFI BIOS I am sure many DZ68BC board users who keep an eye on these forums would appreciate this, having been a long time coming.
Thanks Sylvia - Will keep you posted on any further developments; hopefully these issues will not resurface and my updates can be positive.