keyboard not responding during boot up

**sorry for double post, but really need help**
Hi,

I just recently tried to reformat and now my keyboard stops responding when I first turn my computer on and works when the Windows loading screen appears. I need to do a clean install, but I can't access my bios because of this problem. I was able to get into my bios and disable my hard drive so it would boot from the Windows CD, but after that the keyboard stopping responding and when it said to Press any key to boot from CD, I couldn't. Any help would be greatly appreciated. I've been able to reformat numerous times in the past without any problems. Also, the keyboard works fine after the Windows loading screen, I can do everything as normal. Just can't access my bios or the screen after that says Press any key to boot from CD...

AMD Athlon 64 X2 3800+
2 gigs of wintec 6400 ram
200 gb samsung hard drive
xfx nvidia 7600 gt pci graphics card
windows vista home premium oem
i'm using the microsoft standard black ps2 keyboard and intellimouse explorer 3

i built the exact computer that was listed in the budget system on may 8th here on toms hardware.

again, any help would be greatly appreciated. thanks!