My machine was rebuilt a few months ago with configuration shown at bottom.
It worked fine for a while. But now it boots only part way, then stops and is completely unresponsive to keyboard.

Sometimes I see error code A3, and a BIOS style screen that is just typing, saying F2 to run setup and so forth.

Sometimes I see error code 0D and an ASRock Splash screen with similar message.
In both cases, it does not respond to keyboard, mouse, or anything else.

Sometimes, if I unplug all the USB devices before starting, it boots normally into the Windows 7 screen. I can then plug in USB devices and I'm good to go. But this is not consistent.
In early 2012 there were other messages about A0 and D3 Dr.debug error codes. That's why I got the idea of unplugging the USBs. But I never saw a solution. Possibly a BIOS update took care of it?
Any suggestions?? I cannot even figure out what BIOS version I am supposed to have - version numbers are not listed anywhere that I have found.

thanks!

ASRock P67 Extreme4 Gen3 with BIOS 2.02.1205
Windows 7 ultimate (64 bit)
Corsair XMS3 4GB x 2 memory

Nvidia 460 graphics
Razer mouse and keyboard
Antec 650W power supply

Boot drive = 120GB Corsair SSD
Also several Seagate hard drives