Thanks for your reply.
It is a Seasonic X-460. Scarcely you'll find a better psu in desktop range. It worked 3 months with another mainboard with no issues.
Also I installed a pcie 1x USB addon card, with 4 ports. If I connect any usb device to this card, avoiding mainboard native usb ports, the system is rock solid (although the message persists)...
OK, let's assume for now that it is only software issue.
PART I - get rid of all USB devices
1) Allow Remote Desktop access to machine,
I understand that you are using USB keyboard and mice, but we need to deal without them, that's why you must login to Windows via Remote Desktop,
2) Power down machine,
3) Unplug all USB devices while machine is off,
4) Disconnect all USB devices,
5) Power on machine,
6) Login via Remote Desktop.
PART II - remove all USB devices from system
1) Download the following tool: http://www.nirsoft.net/utils/usbdeview-x64.zip
2) Run above tool with Administrative privileges,
3) Find all USB devices that you can recognize - keyboards, mice, plotters, even USB sticks, right click on them and delete each,
4) Close the program.
PART III - do real driver update
(real, because in normal setup.exe-double-click you will not update all drivers, because setup program incorrectly assumes that update'ing some drivers is not neccessary)
1) Download the newest chipset drivers for your MB from Intel's Download Center (click this link),
2) Unzip downloaded file,
3) Run Command Prompt (cmd.exe) with Administrative privileges,
4) In Command Prompt, go to folder where drivers were extracted (using 'cd' command),
5) Invoke the following command: setup.exe -overall -overide
6) Installation wizard will appear, install as usual,
7) Reboot machine.
PART IV - reconnect devices
1) Connect first device,
2) Wait for graceful installation,
3) Validate for some time if the device is working properly,
4) Connect second device and do the same as above,
5) Connect third device and do the same as above,
... and so on.
I wish you luck and I'm looking foward for your results!
PS Thank you for providing me RAM model - I'm using the same in new servers and was unable to find other brands to consider. I really like Kingston, but I was dissapointed that those modules are based on ELPIDA chips. Some time ago it was Hynix, maybe ELPIDA is OK now, I don't know, there were my first chips based on it. But nevermind, I've tested them really hard and no error occured, speed is also very satisfactory.
And I have replied you about checking ECC availability here: Re: S1200BTLR, some questions
Thanks for you detailed reply. Before trying it, however, I gotta say a thing: USB problems were present even *before* OS installation. If you plug in enough usb deviced, the mobo hangs at bios POST.
Also, I booted with various linux live distros: same usb problems as for windows.
The ram: It is true that ELPIDA is considered a bit "low-end". If you want Hynix chips consider Crucial ecc ram sticks.
Sorry to hear that
Please attach settings from BIOS -> Advanced -> USB Configuration.
This may sound unrelated, but set in BIOS following options:
Advanced -> PCI Configuration
Dual Monitor Video: DISABLED
Wake on LAN (PME): DISABLED
Onboard NIC1 ROM: DISABLED
Onboard NIC2 ROM: DISABLED
...the same for rest NIC ROMs