Pc starts for 3 seconds then trottles and tries to start again

[Damagepersec]

i ugraded my pc case.
Pc starts for 3 seconds . The motherboard says 15 idk what that means no image on screen, fans startup i think all of them then it shuts down and starts up again by itselr and does the same
Gigabyte z87x ud3h M
I5 4670k cpu
Phanteks case
Raider 550w psu

 

[plaintuts]

Recheck your assembly.

Make sure motherboard standoffs are properly placed