Try re-seating the RAM and the video card. If that doesn't work, try just one stick of RAM, then try just the other stick. Make sure all power connectors are hooked up (24 pin on board, an additional 4 or 8 pin on board near CPU, possibly a 4pin molex on board as well by the PCI slots). Also make sure your video card is plugged in (should have either one or two 6pin power plugs).
If the motherboard doesn't post or make any beep codes and your screen stays black (and the monitor power inidcator stays orange) then it's most likely a bad board or bad RAM. Try the RAM in someone else's computer. If you can, try the CPU in another computer too. Goodluck! These situations can always be stressful