I am having trouble with the boot process for my computer. If my
computer is shut down and turned off, it has severe difficulty getting
booted again. When I push the power button, fans, hard drives and my
cd-rom drive all turn on and spin up fine, but nothing happens on
screen ? bios does not boot.

My current work-around for this problem is to turn my computer on and
off over and over again until bios finally appears and begins the boot
process. Once it does finally start booting, bios tells me that my
overclocking settings have failed (even though I?m not overclocking)
and forces me to 1. enter bios to manually correct things or 2. load
bios defaults. I?ve chosen to load bios on each boot and, after doing
such, the computer boots fine. If I leave it on and running it works
perfectly fine and is perfectly stable.

Through a great deal of troubleshooting (I originally thought I had a
dead video card) I have replaced/swapped out most of the parts on the
inside including the motherboard, the processor, the video card and
even the monitor itself all to no avail.

Here?s the relevant hardware stats:
ASUS P4P800-E 
Intel 478 3.0ghz 800mhz fsb processor
Nvidia 5200 video card
2gb ram
Seagate SATA 160gb
CPU temperature is currently 43c/109f
Motherboard temperature is currently 27c/80f
Windows XP Pro

I built the computer myself and it has worked beautifully for about a
year before this started happening. I have no qualms about opening it
up and tinkering with the inside if needed. If you need any other
information just ask and I?ll be more than happy to supply it.

Thank you!

after changing the mother board u have a BIOS problem , then u must go
n replace it , some capacitor must have blown off

In response to aqua06 - 
I admit bios seems a likely culprit here, but both motherboards have
produced the same results. The first one I had in my computer worked
for almost a year without any problems. Then, out of nowhere, things
went bad. So I replaced it with the second motherboard and am still
experiencing the same results. I looked over each board carefully
(because I have burned up mb's before) and I find no visual evidence
of anything scorched/melted/or otherwise ruined. Thanks for your
input!

It sounds to me like it could be the power supply.  What power supply
are you using and what's the wattage?

One of the things that leads me to this conclusion, is you said you've
swapped just about everything else out.  In addition it is possible to
have enough power to turn the fans and what not, but not quite enough
to run the processor.

In response to feldersoft-
I was thinking that too as there's so very little left of my original
computer to replace or swap with old parts etc. Unfortunately, I don't
have a spare power supply to test the theory and wasn't quite ready to
go and buy a new one. It's an Antec TruePower 430w. Its load includes
the following: one sata hard drive, one dvd rom, the
motherboard/processor, video card, sound card, ethernet card, and four
80mm case fans. I wouldn't figure that would be too much, but if
something inside it has tripped out or is starting to go bad, maybe
it's power is fluctuating and causing problems during startup.
However, as one of my troubleshooting steps that I performed earlier
(with the old board - haven't tried it with the new one), I unplugged
all case fans (but not the processor's) along with my hard drive and
my dvd rom to see if I could just boot it to bios and it didn't work.
I suppose it's possible that my original motherboard did die and when
I replaced it I happened to get another bad one with the same problem
(but how likely is that??). "Ghost in the machine" is beginning to
sound like a plausible answer at this point. :) Thanks for your
comment.