Possible dead motherboard?

[ETA_]

Hello,
My PC has been sitting unused for a couple of months but recently i decided to use it again. The trouble is when i turn it on it powers on for half a second and then turns off, and it keeps doing this until i turn off the power supply. The fans start to spin and the motherboard and GPU and case LEDs light up for half a second. I've tried two different PSUs on it both with the same problem. The first PSU I actually put in a couple of months ago, and the PC worked back then.
I tried with 1 stick of RAM, no sticks, without the GPU and then I breadboarded it with just the motherboard, HSF, CPU and PSU. The 8-pin CPU power connector and 24-pin power connector were both plugged in. I shorted the motherboard with a screwdriver and got the same problem, the LEDs light up and fans spin for half a second, turn off and then it repeats.
This PC has been working for many years now, and the only thing that has changed in recent months is the PSU, but i checked both PSUs this way and they seemed to be working which leads me to think it may be a motherboard problem.
The motherboard in question:
Gigabyte GA-X48-DS5 Motherboard

Thanks very much

 

[alexoiu]

Hi, I would try reseating the CPU and the heatsink and replacing the thermal paste.

 

[ETA_]

Hi, I would try reseating the CPU and the heatsink and replacing the thermal paste.

Hello I've just tried reseating the CPU and the heatsink and replacing the paste, I found a tiny bit of paste on one of the pins of the CPU which I cleaned off with a needle, but the problem still persists.
Thanks

 

[alexoiu]

Then yes, possible deas motherboard.