Ok.
So. Here's my issue.

I just bought a nvidia nforce 4 SLI ready intel edition motherboard, a 7300GT PCI Express,Pentium D Core Duo 2.6GHz processor, 1 GB
DDR2 667 stick of RAM, and I kept my previous hard drive and 450 W power supply.

So I placed everything perfectly inside the case,
i even followed the instruction on the
mobo's manual to get everything connected
perfectly.
So I connect the monitor to the 7300 GT and power on the system.
Everything is running perfectly, fans are flowing, LED's are on, Drives are opening, and the Hard drive sounded, like normal, the minute I turned on the pc.
Except for the fact that the monitor LED turns orange
and stays black, as if it weren't even turned on at all.
I double checked everything and I got the same result.
So I switched the 7300GT for a ATI Radeon X1650 PRO and same result.

Any ideas?

Apparently you didn't benchtest the board, so it's difficult to say what the problem might be. Take out all cards but video, disconnect all drives (HDD, optical, floppy) by unplugging the power & data cables, unplug all external devices except monitor & keyboard. Now see if you're able to bootup & access the BIOS.

Nope. Same problem.

Orange LED on the monitor next to the power button
and nothing on the screen.

The next step is what should have been the 1st step...take the board out of the case & benchtest it.

Bench-testing is just setting it up outside the case, and powering on?

Yes, on an insulated surface with one stick of memory, basic video and a keyboard.

Skip

If that doesn't work, a common new build mistake is installing ram that is incompatible with the mboard. If you didn't check out whether the particular ram modules you picked will work for sure in your mboard before you bought them, that is quite possible, and in the worst cases your mboard will not boot, and you may get no beeps at all.

To check for that possibility, remove the power to your case/PS, remove all the ram, restore power, try to boot. If there is nothing else wrong and your speaker is connected so that you can hear mboard beeps, you should hear a pattern of beeps that indicates no ram is installed - e.g. for an Award bios, that's usually a beep for a half second, silence for a half second, a beep for a half second, silence for a half second, etc., continuously.

About the RAM not being compatible with my motherboard, it is.
It's actually the one my mobo is "optimized" for.

And the bench testing doesn't change anything because since its PCI-E, I had to get a new video card so I really dont have "basic" video.
And theres none integrated.
I did try benchtesting anyways but found nothing.

Any other solutions?

Are you absolutely positive it's the correct RAM? Incase you don't know, choosing ram is not just about knowing if it's DDR2 667. You also need to know if it should be Registered or Unbuffered, ECC or NON-ECC.

If you know all that then have you done the 2nd half of Tubesandwires post?

If you have and there's no change then the RAM might be faulty. I've just fixed a machine that would not boot with a faulty stick. The screen remained blank until I moved it to another DIMM slot...so try that and see if anything changes.

"About the RAM not being compatible with my motherboard, it is.
It's actually the one my mobo is "optimized" for."

That statement doesn't tell me anything, and I've heard it all before. It being the right PCxxxx and mhz rating doesn't necessarily mean it is compatible.

Did you try removing the ram? If you get no beeps there is something wrong with your build and it isn't necessarily the video card.

"....its PCI-E, I had to get a new video card so I really dont have "basic" video."

Yes you do. All cards start up in basic VGA mode, even if you have no hard drive.

Assume you've checked all connections.

Tell us more about your PSU. How old/new? What brand? Working recently?

I haven't tried listening for the beeps, after removing the RAM so that might be one thing I can try.

And to Doctor1954,

It's a PSU from a PC i bought about 2 years ago.

a 450W Rhycom.

And it works perfectly with my current build which is
768 mb ram clocked at 333,
2.0 ghz pentium 4 processor.
Nvidia 7600GT AGP 256MB.
80GB Hd.
soundblaster audigy SE sound card.
and I think that's about it.