When there is no signal going to the monitor from the vid card most, not all, monitors will have a sign on the screen that says >no signal< or >check cable<. Now if the power light on the monitor stays amber then there is no signal going to it. If it turns green then there is a signal going to the monitor. May not be video but the monitor is getting some data from the vid card.
Ok now you stated you have tested the computer with several monitors and get the same results. A blank screen. In my opinion the vid card is a flake. Take it back and get another one. Or maybe even before you do that get a known good card and install it. See if the computer gets a picture to the monitor. If not then it's something else. But try those ideas first and let us know how it comes out...