Answer to "No boot, No display, no signal and white power light flashes once"I've just had the same thing happen to my G5 1.8 with 2GB ram. Installed new battery which wasn't the problem then removed some ram(left 512mb in top slot of top two and 512mb ram in bottom of bottom two slots. Machine booted,now backing up while i have the chance as the fans are pretty noisy, the future is uncertain but the plus side is i just got a 2nd chance to save some irreplaceable stuff.
Answer to "Why won't my G5 boot?"Thanks so much for the above post/s, was having the power light come on my G5 1.8Ghz with 2G of ram but that's as far as it went with no screen appearing at all. Ordered & installed replacement battery, which made no difference. Like the post by P.B above I have just removed some of the RAM (but i left matching 512mb's in the top slot of the top 2 and the bottom of the bottom 2) It has fired up first time and I'm now backing up irreplaceable files i thought may have been lost. The fan is pretty noisy now but even if it only works for the next 2 hours i'm grateful,thanks again !