I have this one year old desktop computer P4 2.8 with 512
mb.
My dear dear computer have been serving me with enthusiasm and
working honorably fine but suddenly, when I reset it it wouldn't
turn back on. It never even got to the bios...
I press the power button and the light comes on, Fans turn on, but
it remains at the black screen. No beeps occur either (which makes
me think it isn't a video card problem).
The CPU fan is working...i am thinking, It has to be the CPU or
Motherboard (but i can not test these as I am not a rich guy like
those sgforums P-members and thus do not have any other motherboard
or CPU... 
P4 2.8
512mb
CPU (Fan working)
Graphic Card (Bulit in fan working)
Power Supply Box (Fan running)