Every 3 to 15 days, my PC freezes. This typically happens when the computer is idle, I'm coming home from work, back from vacation, etc. It's never happened while using my computer.

• The monitors are in power save mode
• The Caps Lock light on the (wireless) keyboard doesn't work
• Ctrl-alt-del has no effect, mouse (wireless) has no effect
• The hardware reset button and single press of power putton have no effect
• Computer does not appear on the network
• No BSOD, no memory dump
• Event logs have no errors or indications of problems near the time of crash. Only messages after reboot indicating that there was a reboot without a clean shutdown.
• Windows is set to never put the computer to sleep (just the display)

Here are the vital stats of the build:

• OS Windows 8 Pro 64-bit
• CPU Intel i5-2400
• Mobo Intel BOXDP67DE Micro ATX
• GPU MSI N460GTX Cyclone768D5/OC
• RAM CORSAIR XMS3 8GB (2 x 4GB) CMX8GX3M2A1333C9
• PSU SeaSonic X Series X650 Gold
• System Drive Samsung 840 Pro 256 GB SSD
• Data Drive 2 x Western Digital WD20EARS 2TB in hardware RAID 1
• Optical Lite-On DVD burner IHAS424-98

And here is the story of how the problem developed and what I've done to diagnose:

• January 2011, system built with Windows 7 64-bit, runs great.
• March 2011, Intel replaced the mobo because of the bad sata controllers.
• October 2012, upgrade to Windows 8 (problems start shortly after).
• January 2013, system freezes and causes network to fail for the whole house. Unplug the network cable and other devices and PCs can use the internet. Plug it back in, internet goes away for everyone. Reboot and everything is fine.
• March 2013, install Intel Gigabit CT PCI-E NIC, disable mobo nic in bios. Network strangeness goes away. Freezes are less frequent.
• Memtest shows no problems (20 passes).
• Early June 2013, replace Antec PSU with SeaSonic PSU.
• Mid June 2013, replace OCZ Vertex 2 SSD with Samsung SSD.
• Late June 2013, get frustrated and hope the community has some good ideas (I'm running out of budget to replace parts).

My next plan of attack is setting "Turn off display" to Never and using a screen saver to see how that reacts on the next freeze. It makes me sad to waste power for up to 15 days though.

Has anyone out there seen a problem like this? Any ideas on what kind of malfunction would act this way? Ideas of other diagnostic steps to take?