|My experience with this issue is that the problem is a timing hazard:|
Basically anno-2010 computers run through BIOS so fast that the USB keyboard does not have time to reset and bring up the USB connection before the BIOS is past the point at which hiting DEL will bring you into BIOS settings.
The problem *may* have to do with me using a (USB) KVM switch that resets the USB connection very late/slowly (or perhaps the slowness is on the PC side, I can't really tell).
Anyway, the telling symptoms are that the keyboard LED indicators will flash (NumLock-CapsLock-scrollLock) sometime AFTER the BIOS is done and I'm already in the bootmanager menu. At this time the USB keyboard starts working.
As other people have said, directly attached and even KVM-attahced PS2 keyboards will still work, and the reason I believe is that they do not take a long time to reset a connection.
Only a few years agio, BIOS used to test the memory on startup, and you would have to hit ESC to bypass it. This hid the keybaord problem even for a USB keyboard, I think. Many 2009-2010 motherboards do not even have an option to turn on memory testing, because memories are now routinely so large that the testing takes too long. Too bad.
Quick fix: Have a PS2 keyboard handy if you need to get into BIOS
Good fix: none that I know, not even sure that bypassing the KVM is enough to get the USB connection up in time. I don't have a spare USB keyboard to test this right now -- can someone please do the experiment?