DQ77MK: USB and network failures under Win7, unable to flash BIOS

System specifications:

• Windows 7 SP1 Professional x64
• Intel DQ77MK motherboard
• Intel Core i5-3570 processor (not the K model, as I require the virtualisation features) (passes Intel's processor diagnostic tool)
• 8GB DDR3 1600 (2x4GB) memory (passes memtest86+)
• Generic Dell keyboard and mouse (both USB 2.0)

First of all, my board's BIOS is dated 11/20/2012. Regarding trying to update it with the latest revision today:

• The express method (MKQ7710H.86A.0064.EB.EXE) does not work.
  • After running the updater, the system reboots, enters S3 for several seconds, and then proceeds to boot normally (with no change to the BIOS version shown during POST).
  • Upon rebooting back into Windows, the updater claims that the flash was successful. However, the actual BIOS remains unchanged, as reported by both the BIOS itself and Intel Desktop Utilities.
  • No reports of a failed flash are recorded in the BIOS event log whenever I try this method.
• The recovery method (MK0064.BIO) does not work.
  • After confirming that I want to update, the system reboots, enters S3 for several seconds, and then proceeds to boot normally (with no change to the BIOS version shown during POST).
  • The BIOS remains unchanged, as reported by both the BIOS itself and Intel Desktop Utilities.
  • A failed flash message is appended to the BIOS event log every time I attempt this method.
  • I have tried this method using different types of USB drives and CDs.
• The Iflash method (MKQ7710H.86A.0064.BI.ZIP) does not work.
  • After confirming that I want to update, the system reboots, enters S3 for several seconds, and then proceeds to boot normally (with no change to the BIOS version shown during POST).
  • The BIOS remains unchanged, as reported by both the BIOS itself and Intel Desktop Utilities.
  • A failed flash message is appended to the BIOS event log every time I attempt this method.
  • I have tried this method using different types of USB drives and CDs.

Other steps I have taken (had the PC unplugged from mains power and took ESD precautions where applicable):

• Running the express updater while in safe mode.
• Removing all add-on cards and external devices except for the keyboard, mouse, and a DVI display.
• Draining capacitors on the board by holding down the power button on the case for 30 seconds.
• Removing the CMOS battery, draining the caps as per above, and then inserting it again.
• Changing the duration that the system stays in S3 during a flash to 20 seconds.

I am uncertain if the problems I keep experiencing in Windows are linked to the outdated BIOS, as in the past I used to only have trouble with just the 82574L adapter once every few months (when it failed - always with Code 43 - I would just switch the ethernet cable over to the 82574LM adapter until the next time I rebooted the system).

After a period of the system being on - almost always between 30 minutes and four hours:

• Both onboard network adapters (82574L and 82574LM) cease proper functioning:
  • If one of the adapters was in use at the time, it gets a metaphorical boot to the head, with its status in the device manager changed to:
    "Windows has stopped this device because it has reported problems. (Code 43)"
  • Any onboard network adapters that were not in use at the time (no ethernet cable connected to it and another device) remain reported as working properly in the device manager.
  • Regardless of their reported status, network connections can no longer be made with either adapter.
  • The system event log starts getting spammed with this message (all from SharedAccess_NAT and with ID 31004):
    "The DNS proxy agent was unable to allocate 0 bytes of memory. This may indicate that the system is low on virtual memory, or that the memory manager has encountered an internal error."
• All USB ports (even ones on add-on cards) stop detecting changes:
  • USB devices that were already attached continue to function properly (e.g. keyboard, mouse, drawing tablet).
  • If a new USB device is inserted or an existing one is unplugged, there is no change in the device manager; removed devices remain visible, and new devices never appear.
  • Scanning for hardware changes causes the "Scanning plug and play compliant hardware" message to appear indefinitely.
• ACPI functionality seems to break:
  • If I try to shut down or restart the system, Windows hangs at the "Shutting down.."/"Restarting..." message (with the activity indicator still spinning).
  • The physical power and reset buttons on the case no longer act as they should. Per my configuration in Windows, pressing the former should trigger a normal system shutdown. Per the design by the case manufacturer, pressing the latter should immediately cycle system power without a safe shutdown.
  • However, I can still hold the power button for ten seconds to forcefully power everything off.

Any ideas?  I'm more concerned about the inability to update the BIOS at the moment since the other issues could be driver-related.  Sorry for any inconsistencies/typos, I wrote this in a bit of a hurry.

Cheers.