**Update** The problem I posted about below seems to have developed into the Mac simply refusing to turn on if the monitor is plugged in now. If I unplug the monitor, then plug it back in the Mac turns on, emits a loud long beep, during which the power light rapidly flashes. The big fan inside then goes into overdrive for a few seconds before calming down and then the Mac boots into Open Firmware. I can then type mac-boot and the Mac boots into OS X and has no further issues provided I don't shut it down. I can put it to sleep and wake it from sleep but if I shut it down, it won't turn back on again unless either I unplug the monitor and press the power button, or I plug the monitor back in. I've tested the PSU and it seems OK but I've not completely ruled it out. I've also used a completely different (but identical) acrylic 23" Cinema HD display, and also swapped the graphics card for a different working one (a Geforce Ti as opposed the 9000 Pro that was in it originally) and neither has fixed the issue. I've reset the PMU several times as well, and tested the backup battery (it shows 3.7v so might be OK), all to no avail. **original post below** Hi, anyone can help? I have an old acrylic cinema hd display, 23" (M8536). I use it with a june 2003 mirror drive door powermac g4. It seems to have developed an annoying habit of turning itself off randomly. Though I don't know if it's the monitor that's the problem or the mac (I can't test it on another mac to find out). When it first did it, it just went off and the power light on it started to flash, so I unplugged it and plugged it back in a few times then after that managed to restart the mac a few times too and it seemed to work fine again for several days of use. Then today it's done it again, worked for all of 30 seconds after turning the mac on and then just went off only this time th epower light didn't flash, monitor seemed completely dead and couldn't get anything out of it. Again, unplugged it and plugged it back in, power light came on, then went off again, screen still stayed black. So, I pulled the power on the mac and I've left it now. I haven't tried it since but I figured I'd ask if anyone's got any ideas on this. Googling seems to bring up a lot of similar problems but they all seem to be about more modern versions of the monitor rather than these old acrylic ones.