Hello, my first question after failed googling to resolve this issue. Apologies if I have missed it!

After I shutdown OS X, which works fantastic, I switch on my PC again, where during the bootloading process of OS selection, my USB keyboard does not respond. It will only begin working again if I allow the system to auto boot OS X, where the keyboard becomes repsonsive once OS X starts again. If I restart OS X, not shutdown, the USB keyboard does work in the boot loader process. It's a minor problem but and inconvenient one. Anyone can assist? Many thanks.

ZEP 10.5.2 rev 1
AMD 4200 sckt 939
Nforce4
Microsoft USB keyboard