After extensive testing I have narrowed down a problem where both Windows 7 and Ubuntu Mate 64-bit won't boot with "Load Optimal Defaults" option in BIOS and a USB HUB plugged in (TA790GX3 A2+ mobo, Phenom 9950BE CPU,4 Gig RAM and GeForce GT 620).
The BIOS "USB Configuration" is:
Legacy USB Support - Enabled
USB 2.0 Controller Mode - HiSpeed
BIOS EHCI Hand-Off - Enabled
With these settings, Windows boots to the point where it says "Loading Windows" (logo never appears) and Linux fails during kernel initialization with no messages.
Any one of the following will allow the computer to boot:
Disconnect external USB 2.0 hub.
Disable Legacy USB Support (no way to enter BIOS with USB keyboard).
Set Legacy USB Support to AUTO with no attached USB devices.
Set the USB 2.0 Controller Mode to FullSpeed (USB 1.1).
Disable EHCI Hand-off.
Disabling Legacy USB support is not an option since I have a USB keyboard and mouse. Disabling EHCI handoff prevents Hibernation from working properly. Disconnecting the USB HUB until after windows boots is not convenient. Setting the USB 2.0 controller to FullSpeed makes booting from a USB device annoyingly slow.
Windows 7 and Linux both load drivers to support USB OHCI, EHCI, xHCI, etc. so it doesn't matter if the BIOS Legacy support is enabled. Even the initial setting of the USB 2.0 controller is superseded and eventually the OS sets it to HiSpeed. It appears that some sort of low level hand-off between the SB750 south-bridge and OS is causing the hardware bus to hang during initialization.
Testing was accomplished with FE2.1, GL850G, and UPD720110A based USB HUBs. Boot always fails with a USB Mouse and Keyboard attached to any HUB. The FE2.1 causes failure with nothing plugged in, whereas the UPD720110A works with nothing plugged. While certain HUB chip-sets may allow the system to boot, ultimately, numerous I/O devices, like a keyboard or webcam, cause failure.
From a hardware standpoint, some users suggested that power or Interrupt Request (IRQ) conflicts might cause this issue. A flaky power supply could induce any number of problems but it's doubtful the boot failure would occur solely, and consistently, at the point where BIOS hands off to OS.
x86 based IRQ architecture was notorious for conflicts because it provided only 15 lines for all hardware. Often a user would have to hard set the IRQs, and disable Plug and Play functionality in BIOS, or override settings in the OS (Windows 95/98/ME), to get devices working. Those problems seemed to slip away around the time of Windows XP, 64-bit architecture and PCIe. Regardless, no legacy IRQ BIOS settings are in effect and there are no overlapping IRQs, or even use of any, below 15.
At this point I have no solution to the problem. The most promising work-around is to set the USB Controller to FullSpeed. It's interesting to note that my other computer, comprised of TA780G M2+ mobo, same CPU and memory, boots fine with default BIOS settings.
