motherboard - Asus Z87pro: After re-install Win7 blue-screen on starting any game

Not my own rig, but that of a colleague.

Asus Z87 Pro based gaming rig. 32 GB RAM, 2x Samsung 840 SSD, Core-I5 (4670), 750W Antec PSU, Geforce GTX 780.
System has been stable running Win7 Ultimate x64 for about a year.
Daily used for gaming and media-center.

Last week he re-installed Win7 from scratch.
There were no hardware changes at all.
As far as I can tell he did everything right regarding drivers. (Motherboard drivers, Sata, LAN, video, audio in that order. Didn't use drivers from the original CDROMs that came with the hardware. Pulled latest drivers straight from the chipset manufacturers.)

Now as soon as he launches any game the system will BSOD, without logging any reason in eventlog. After re-installing the GeForce drivers it got slightly better. Sometimes games will start only to fail after 10 minutes or so.

EDIT It is NOT a BSOD. The Asus Surge Protection in the Bios causes the system to shut the power off. After that it starts automatically because of the Bios setting "Resume after power-fail".

Before the re-install the system did NEVER do this. The system has been used for a while with 2 of these Geforce GTX-780 cards without issues as well. (So the PSU should be able to handle the load easily with just one of those cards.)

System is stable and running fine with just desktop use and when streaming media to a TV. Very strange situation.
How best to troubleshoot this issue?

P.S. This might be related, but it doesn't seem likely.
This particular motherboard has an issue with the clock that stalls while the system is running. (You set the time, but after 40-60 minutes the clock just keeps hanging and doesn't update anymore. After a reboot the clock works again.)
My colleague re-installed Win7 in the hope that would fix the clock issue. (If he had Googled he would have found out that it is a known structural problem with some of these Asus boards and he needs to get it replaced under warranty.)
After the re-install the BSOD problems began, the clock is still stalling.
From what I get from Google this clock issue is not known to cause BSOD problems.
EDIT Asus released a Bios fix for this clock issue on 23/6/2014.

I recommended him to get the mb replaced anyway while it is still under warranty because of the clock problems.
(EDIT Doesn't seem necessary now.)
But still it is worrisome that something else might be wrong with the rig so he would like to get to the bottom of this.

Any ideas on how to proceed are welcome.