Then it comes down to a failed component. To rule-out:
1. RAM boot with (1) stick; failure try another ; failure:
2. Remove the GPU and if possible use an iGPU (onboard video). You can also boot without a GPU and 'sense' (sound and looking at components) if the PC can boot. Otherwise try a different GPU ; failure:
3. Try a different and minimally sized PSU for your PC. Choices: (a) from another PC or (b) local store offering an open box or with a good/acceptable return policy ; failure:
4. Disconnect ALL peripherals including Mouse, Keyboard, HDD and DVD, and all USB devices and USB headers connected to the MOBO ; failure:
Now it get complex, the failure rates for MOBO 80% and CPU 20%. A local PC shop can diagnose the problem substituting parts to determine the failed component(s).