0. Is your monitor connect directly to the motherboard? Remove your GPU since you don't need it to boot up
1. Did you hear any beep? Sometimes the mobo will beep out (1, 2 or 3 beeps) for error issue. I guess you need speaker to hook up to mobo to be able to hear it.
2. If you already did a quick check on cable connection, the next step is just try 1 module of memory at one time. If it does not work, try different slot. If no luck, try the other memory module.
If the above 2 quick steps don't work, here is the full procedure.
3. Here is the link to PC troubleshooting guide that someone created so I just link it for you to follow.
http://www.tomshardware.com/faq/id-1893016/post-system-boot-video-output-troubleshooting-checklist.html