Randomly but quite often, after booting my PC the USB3 ports (Etron chip) do not work. They don't even show up in Windows Device Manager.

Second issue I've been having is boot failures. On average maybe one boot in ten fails. The error code shown by Dr. Debug is always 94. According to the manual it means "PCI Bus Enumeration".

The only thing I've added to the bus is graphics card, Other devices are provided by the motherboard. That's why I'm thinking maybe these problems could be related.

I think it's not a driver problem since even a USB chip without driver should show up in device manager. Does anybody have any idea if it's a Windows problem, a BIOS problem, or a hardware problem with the motherboard? Clearly, the boot problem can't be a Windows problem. If the two problems are related this means the USB problem would also be either BIOS or hardware problem.

Any ideas what to do?

My system:

Asrock P67 Pro3 (BIOS 2.00)
i5 2500K
GeForce GTX560 Ti
Windows 7 Ultimate 64-bit
4GB memory