Gotta do problem solving 101 at this point.
Unplug everything except the CPU/Cooler and the PSU. Then power it on. You should get beep codes for the RAM and GPU failure (maybe. you may not get any beep codes with no RAM installed.) If it continues to POST loop like it is, then it could be a mobo or cpu issue.
I would continue on anyways just to verify. Stick 1 RAM stick in and power it up again. Beep codes or POST loop again?
If POST loop again, then things are looking bad. If beep codes then that's moving in the right direction.
Put in 1 GPU and power it on. At this point it should either fully boot or continue to loop. If it's still looping, then move the RAM stick into different slots. Once you exhaust that option, start moving the GPU into different slots.
If after doing all of the above you still get the POST loop then it looks like either mobo, cpu or psu are bad. Swap them out if you have spares around and see if anything changes.
Make sure you have no peripherals plugged in. No mouse. No keyboard. No wireless dongles. No drives of any type. We're just looking for a successful POST at this point.
EDIT: Also make sure you have the 4 or 8 socket plug for the CPU plugged into the mobo from the psu. I have failed to do that on many occasions which led to a lot of unnecessary troubleshooting.