Help!! I built my first. Pc ::( ?

I built myself a pc yesterday I though woo hoo great built seemed like done everything write. Turn it on hmmm.. The screen went no signal. So turned it of checked the gpu and cables are in snugged in and secure. So tried again. Still same prob. Maybe my gpu n power are compatible or motherboard . My psu is a arctic 700w mb asrock m3a770de and gpu xfx is ati hd 1 gb 5670