BleepingComputer.com: Need Help Please!

Okay I'm not very computer savvy so I apologize in advance if I seem a bit slow. Here is my problem however. I have a Compaq Presario 5423 Desktop PC that I received from a friend a bout a year and a half ago. I added a second hard drive, and used it for about a year. After a year I got a laptop so I stored my desktop in the bottom of my closet. It's been there for around 6 months. Well yesterday I took it out to hook it up, I was going to give it to my father, but it no longer works! I took the cover off the case, and heres what happens.

When it turns on, everything appears to be booting up as it should. The processor fan kicks on, the hard drives start up, the disk drives will open and close, the keyboard lights come on for that brief 2 seconds, the monitor goes from standby mode to power on mode, and then thats it. Nothing more happens. Nothing load on the screen, nothing at all.

I've been trying to get help from so many people, I've tried the following list of actions:

Removed the CMOS battery for 12 hours to reset it
I moved the jumper on the CMOS to reset it
I have completely unhooked everything and rehooked it up including taking the motherboard out of the case
Checked all connections, and reseated all cards, ram, etc

I am so clueless as to what is wrong and how to fix it, someone please please please tell me what to do, and I pray at the same time it's an easy fix.

Do you see the initial black and white screen?
Can you access the BIOS
Do you hear a post beep?
Does the computer remain running, just nothing showing on the monitor?
Try a different monitor. Make sure the monitor is securely plugged in. Check the monitor cable for bent pins