As a rule you should always provide your PC with a clean uninterruptible power source.
I know this is not the solution but it's a step in the right direction which will eliminate your problem.
If you have electric cut offs in your country then, a decent UPS is your answer.
Thanks for suggestion, the problem is not in electric cut offs, but in system specification. I have this PC build-in in a bigger system, which needs to be powered off completely when not used. When this happens, power is cut off by a switch for whole system in less than one second. PC is connected behind UPS, so when UPS detects cut off, it turns off PC in non-damaging way and then it turns off itself as well, which causes power cut off for PC.
Since in system specification is that it has to be able to turn itself off completely, I cannot leave UPS on (and it would run out of power eventually anyway).
I believe this is a normal behavior since I have seen something similar before but I am not exactly sure about that boot delay you are getting during the Intel® splash screen; I would probably have to test this just to make sure. Do you get the same results with different BIOS version?
I have tried two versions (156 and 160), and I haven't noticed difference. If it is normal behavior, is there any way how to display some text output about what is going on at the moment? Like this, it seems that PC just froze...
There is no more POST on-screen display besides the hexadecimal POST codes on the corner; however, you may check in the BIOS event log. Can you provide more information about your system configuration?
The hexa POST code does not change, it is the same for both quick and "frozen" boot. I'll try the log again, but I think I have already looked there and only event there was something with chasis, dated to PC assembly time.
Configuration is pretty much basic, Core i3, 2TB HDD, 4GB ram, mouse, keyb, some custom USB peripheries - I have tried booting with those disconnected and there was no difference. If you need more detailed info (frequencies, component manufacturers/models, ...), please let me know what exactly might be helpful.
Something like: processor model, RAM model or clockspeed and voltage, power supply wattage or model, any other internal device connected to the motherboard…
Sorry for delay, I was away from office for some time. Towards the PC specs:
CPU - Core i3 2130
RAM - 2 x 2GB Kingston DDR3 1333MHz CL9
PSU - It is Chieftec CD-01B-B case with built in 350W PSU, I believe the model is GPA-350S
There was no OC, so all voltages are on default levels. No other internal devices are connected to the board.