No pic on my monitor

I have a compaq presario. The monitor stopped working and I started checking to see if it went bad. I put it on another PC and it works like a charm. I then put another monitor that I KNOW works and attached it to the compaq but it too does not come on. The power light will light up and in two seconds it clicks off as if its asleep. The keyboard sleepmode light lights up. I know that its not the monitor. I do not know what the graphics card looks like. I found two things that look like memory and clip in like memory but instead of being near the back of the computer on the mother board they are near the front and go up and down rather than horizontal. I think they may be what is called the sound card or video card. I just don't know where to go from here. I did take the CD and DVD (which I recently added) and disconnected them. The monitor still doesn't come on. I dont know if I should try to disconnect the hard drive and try it but someone said it might be the video card...I just don't know where it is or what it looks like..or if that sounds like the problem...like I said the monitor comes on when attached to another computer and when I attach a good monitor to the compaq then it will not come on either...Any help or suggestions are greatly appreciated...