Computer wont turn on - Motherboard problem?

Hey guys,
For 1 month now, my pc started only if I turned off the PSU, waited 5-10 seconds, then turned on the PSU and pressed the power button (this started to happen after I cleaned up inside the case). But, this morning ,trying to do the same, nothing happens. I powered up the PSU with a paper clip and it starts, my mouse has power since the led is on.
When I do the "off/on" trick, and press power button, one of my systems fans receive an impulse only, then nothing moves. What could it be? Tried even to start up the pc without the power button directly from motherboard (maybe I failed on that somehow ... ), reseted BIOS, tried with only 1 memory slot.
Is there anything else I can try or ?

Motherboard: Gigabyte GA-MA-790X-DS4
PSU: Recom POWER ENGINE RC-450