hii...... back to basics.... disconnect all drives take out the graphics card so that all you have is the motherboard and ram ...see if it posts !!!
remove power to motherboard before following each of the next steps !!
no post ???? remove the ram stick ,do you then get bios beeps ???
no beeps ??? check the cpu is seated correctly .
bios beeps heard ? reinstall ram stick make sure it seats properly ... a successful post should hear a single beep from bios ...then add one componant at a time checking for post each time.