My Mac will not turn on easily, shuts down often

Question

I have a G5 -- Mac OSX 10.3.9, about 4-4.5 years old now.
Some months ago, it began to shut down seemingly for no reason at all. I could only keep it from randomly shutting down by leaving iTunes or something else on, so that some process was being carried out (I believe that the idleness caused something to trigger, though maybe it is just coincidence).
Recently, the computer has been refusing to turn on easily, if at all. I have to push the "on" button sometimes as few as under five times, and sometimes as many as several minutes worth-times for it to finally "click," and turn on. The problem seems to be getting worse (it took me a lot of clicking the "on" button to get it to turn on just now).
Also, it seems that if it was on recently, it is significantly easier to turn it on the nest time.
Any help with what the problem might be and how to repair it would be very much appreciated.
Thanks.

Answer 1

There's a system management controller - or some such reset button
on or in the computer, it is a second cousin to the Power Management
Unit (PMU) found in G4 machines and somewhat related to the next
version found in the newer Intel Macs.
The chip, by whatever name, contains information essential to the
basics of power management and other stuff, and there are times
where that may be corrupted so resetting it may be helpful.
Depending on what computer model you have, the procedure to
reset the chip will vary. Within a processor series, it will vary...
So, to approach the reset correctly, one would need to know the
exact model and build the computer you have... Or close.
This chip has also been known as a CUDA or PMU, SMU, SMC,
and so on; as such the PowerPC based units often had one
series of power management chip with variants, and the Intel Mac
architecture has something similar yet different.
"Resetting Cuda/PMU on Power Mac G5, Power Mac G4, PM G3:"
http://support.apple.com/kb/HT1939
If you have an iMac G5, the information would be different.
For Apple Portables, depending on architecture and series...
Resetting the System Management Controller (SMC) & PMU
http://support.apple.com/kb/HT1411 (note PPC-PMU inside link)
Generally speaking, information for most Mac power reset chips
is listed here, in this page, with secondary links to information:
Resetting the power management chip in your Mac
http://www.thexlab.com/faqs/resetpmchip.html
{And if the hard disk drive is getting overly full, there are issues
and symptoms of sluggishness and irresponsiveness related
to that situation; you need plenty of free space for OS X to work.}
This may help. Depending on what model G5 you have, it really
could make a difference. At any rate, I'll always think it should've.
Good luck & happy computing!