In article <110720042147181383%fsnet.co.uk>,
Picman <fsnet.co.uk> wrote:
While it could indeed be hardware (motherboard or bad RAM even a
monitor,etc and once you have eliminated these) it is worth it to try
Disconnect ALL external addons (USB & Firewire SCSI hard drives scanners
DVDs CD burners etc). While keyboard & mouse are not likely candidates
here, if you have others try them later too.
Open Mac case (with power off but power cord still plugged in).
Once case is open, touch the power supply case to remove any stray
static electricity charge your body may have before touching any other
If you have added RAM, remove the newer added RAM.
It would not hurt to make sure all internal cable connections are good,
by removing & reseating all such cables, especially those which connect
to the motherboard.
Replace the PRAM battery on the motherboard. This is a 3.6 volt lithium
battery readily available at computer supply stores. A dead PRAM battery
can prevent boot up or video on monitor.
Near the battery on the motherboard is a PMU (Power Manager Unit -- on
older Macs this was called CUDA hardware reset button) button. Press
this ONCE (too many presses might leave PMU in unhappy state and can
drain a new PRAM battery with hours rather than 3-5 years).
On start up reset PRAM by pressing Command Option P & R keys
simultaneously. I think you need to hold these buttons down until Mac
chimes 3 times. This PRAM reset is likely already down my the PMU reset
but do it anyway.
Hopefully your Mac will boot successfully after all this. I had this
problem occur several times (about 3-4 times total with the two G4s)
with both a G4 450 and a G4 933. Most times this happened after power
outages when G4 was on. Once it happened after I had case open replacing