Open Firmware Startup Manager freezes

I have Ubuntu and Kubuntu successfully installed on two different
partitions on my NewWorld computer. Whenever I hold the option key down
and try to use Open Firmware Startup Manager, if there is a linux O.S.
present, whether on a CD or installed on the computer, Startup Manager
gets stuck. It shows me the Mac O.S.s and Linux with the pengiun image,
but it gives me the spinning disk and doesn't proceed from there. I
have given it several minutes but I'm never able to do anything. As a
result I can't boot up my installed Linux. Does anyone have any ideas
about how to deal with this?

Thank you.