Another question... are you sure the monitor works? Never assume a part works just because it's new or was working earlier, even with a different system. Check and double check each part you test. You can easily spend hours and lots of money getting new parts just to find out your monitor was dead in the first place.
Technique I use when troubleshooting, always check the most simple things first. Make sure all connections are good, then test the monitor, vid card, and all, slowly making your way to more and more complex problems.
In school i was the system admin for the vocational school, and in the printing class I would get complaints daily about printers not working, and 9 times out of ten it was either a) not plugged into computer and/or wall, or b) no paper in the printer. It was rarely a more complex problem than that.