I've tried to net-boot the latest NetBSD 1.6 for PREP architecture
(ftp://ftp.netbsd.org/pub/NetBSD/NetBSD-1.6/prep/installation/floppy/sysinst.fs)
But all I got was a blank screen after loading the file.  The monitor
dectected lack of signal.

The machine is a Bull Estrella and the boot screen says PowerPC 604e,
200MHz.

Is there anything I can try to make it boot?

Cheers,

-- 
walter pelissero
http://www.pelissero.org