The screen remains black and there is no warning beep. The computer has been running reliably for 6 years and I have not performed anything special on it recently: no BIOS update, no hardware change, no re-cabling... The only potential cause is that we are drying some walls in the apartment and there are a lot of current-hungry machines running concurrently, occasionally causing the circuit breaker to fall and hence power outages. I have tried replacing the CMOS battery but it does not seem to have an effect. The problem first appeared as a screen freeze while my son was watching a video on YouTube in the early morning, then systematically at all following boot/reboot attempts.
The motherboard is a intel DZ77BH-55K (with intel chipset Z77 Express and CPU socket LGA1155) with an i7-3770K CPU (4x3.5 GHz and 8MB cache) with original CPU fan and two Kingston Technology (8 GB DDR3 1600MHz) RAM units. The PSU is a Cooler Master GX 650W Bronze and the graphics card is an ASUS GeForce GTX660-DirectCU II with 2GB of GDDR5 memory on it. The boot disk (with Windows 10 OS) is a SSD 250 GB SAMSUNG 840 Evo while two Western Digital Caviar Blue WD10EZEX 1 TB HDD are installed in RAID configuration for data. There are also a Lite On IHBS112 Blu-ray disk recorder and SAMSUNG 118AB/BEBE DVD ROM player installed. Additionally, a WiFi PCI adapter Edimax EW-7711In is plugged, but I cannot imagine it to play a big role.
I know that this is difficult, but could you document the POST code sequence prior to the point of hang? If it is happening too fast to write down, make a video with call phone.
In many cases, the POST code shown at hang is the last completed operation. POST code 0x14 is part of the Platform Early Initialization (PEI) sequence. It is unclear from the example POST Code sequence whether this is followed by memory or PCI bus initialization. Two experiments to perform: