try remoing the memory and all devices just l;eave cpu, gfx card and thts it see if it boots then.

try another gfx card.

has it also got an onboard gfx card if so boot it off tht first as it maybe an option eithger in the bios or a jumper setting on the mobo itself.

also have u got the small power connector plugged in (not the main power to the mobo) on the psu there'll be another small power connector. if u aint to sxure wht i mean i'll get a pic of it for u