Here is a gift from ... ... ... Us.
Read this document VERY carefully AND read your mobo manual VERY carefully ... especially ALL diagrams for ALL power connectors.
You should have read this document BEFORE you started building but it is not too late.
Skip NO steps .. make NO assumptions (there really could be a standoff shorting you out!). .. Most common causes for your symptoms ...
1) Not all power connectors are plugged in &/or are not fully aligned and seated.
2) Ram or GPU (etc.) not fully/properly seated.
... Lots of other things, too. Read .. beleive ... DO ! . http://www.tomshardware.com/forum/261145-31-read-posting-boot-video-problems