I have a Gateway GT5032 and it won't post, it does not beep or anything!!!

Specs:

RAM: Installed: 1024 MB 400 MHz (PC3200) DDR memory (two 512 MB modules)
Expandable to: 4 GB
CPU: AMD Athlon™ 64 X2 dual-core processor 4200+

* 2.2 GHz
* 2000 MHz front side bus
* L2 cache: 512 KB x2
MOBO: Foxconn C51GU01 Motherboard

Symptoms:

PC won't boot at all!

Automatically tuns on when power is connected to Power supply

The only thing connected to the mother board is the power connectors, CPU, CPU heat skin, CPU fan, and RAM. When I try to turn off the PC I have to hold the power button for 6 seconds. I tested the RAM on an other machine and it's fine.

I made it work for one day. I took it apart completely and rebuilt it with the same parts and wola! it worked!!, but next morning I powered it on and it was dead once again.

I think it all comes down to 2 things: the Mother Board or the CPU.

I need help or tips can some one explain to me why did my computer decided to work when I reseated everything and the next day it broke? and oin addition can some one give me tips or help me trouble shoot if it's something else like the BIOS??