dual 2.3 g5 ppc wont power up

hello today my g5 wouldn't wake up from sleep mode. i tried pushing the front power button but nothing would happen. I turned of my power bar to get it off. when i tried to power it back on nothing happened no sounds or lights went on. I left it alone for about twenty minutes and tried the power button again and it powered up. it was working fine after it powered back up so i decided to shut it down and see if it would power back up but it didn't. any ideas?

Try resetting the PMU. See this Apple KB article: Link

Regards.

its a tower not a laptop. its weird i left it alone all night and it powered up again. now i'm scared to shut it down or put it to sleep.

Very similar to resetting the SMU:-

How to reset the SMU on a Power Mac G5 (Late 2004) or Power Mac G5 (Late 2005)

Also reset the PRAM and/or replace the battery:-

G5 Startup Problem - Mac Support

well i changed the battery and nothing changed so i brought it in to mac station to get fixed. I'll let you guys know how that goes.

so after over a week at mac station I got a call today saying my computer was ready and that the power supply needed to be replaced. well i got there and my computer was waiting for me at the desk. oh how excited i was to finally get it back home and where it belongs. They were quick to tell me it cost $350 and it was working fine. I asked them if i could try it out before i shelled out the money "why it works fine its been on all day" was what i was told. I said if it works fine then let me try it. sure enough when they hook it up and try to turn it on NOTHING. Now they say they have no idea whats wrong with it. I thought these people were supposed to be apple techs. Their nothing more then bad mechanics changing parts they hope will fix the problem. They say I should replace the motherboard. $1200 repair. I wouldn't bring my computer back there for them to change ram. I'm very disappointed.