So possibly it is the next step blocking.
Can you compare to Mandriva One (that you said worked)
and see what the next step should/could be?
I do not have Mandriva 2006 Free Edition to be sure
PS: In Mandy 2006 free edition, if you press F1 or F2 at
the very beginning do you get a screen with options
for the boot parameters?
I also suggest you disable the NIC and firewire cards in
the bios and see if this makes any difference.
My guess is that you have a video driver issue.
So the first thing to try would be to test the generic vesa driver:
add to the commandline
xdrvr=vesa
or something of the like
I think the correct syntax is
video=vesa
if I remember well
http://www.tldp.org/HOWTO/BootPrompt-HOWTO-5.html