So I just built a customized computer via ebay, with the following specs:

http://www.ebay.com/itm/391403143839

Yes, I am AWARE there is no GRAPHICS card and aware there is no OS system. I put in a r9 290x radeon 4g in myself and have a windows 7 disc.

So today it all came and I set it all up but it would give me the "no signal input" error, despite it showing me what was going on on the monitor just fine, but then as I have to boot the system up for the first time with my windows 7 copy, the computer is not responding to my keyboard. Any command I try, nothing, and my keyboard wont even change lights when putting into caps lock or not. Obviously if I can't tell my computer to boot, it's useless. I tried wireless and usb wire keyboards, but still NADA. Any IDEAS on WHATS going on? Make sure you are connecting your monitor directly to your graphics card and not the motherboard.  If that fails take your card out and try connecting directly to the motherboard.  If it doesn't work in the state that it arrived in using the onboard graphics, then I'd send it back.