The socket looks good. Here is a pic that may help

I have a Gigabyte EP43-DS3L that I picked up very cheaply not too long ago. It came with a CPU, and all four memory slots were full - I assumed that it was ready to go. But it would get as far as the splash screen and lock up - you couldn't get into the BIOS, and it would just power cycle again. I finally realized that the person I bought it from had just stuffed some random DDR2 into the slots, and that board wouldn't POST properly with PC-4200. I picked out some PC-5300 memory, and it finally booted.

I had a video card die in it, and it wouldn't post when I replaced it with another PCIe card - I had to stick a PCI video card in it to get it to POST; only after having done that was I able to put in another PCIe video card.

Thank you both for the answer, unlucky that picture is too small to check the stuff around the socket, it was the best I could find with google.
The sockets pin seems fine to me either.
Now as soon the psu is turned on from his back button the mb turns on, no need to push the power button, this is going to be curiouser and curiouser...
I took some other pictures: https://imgur.com/a/CeB7zek

Are you sure your power supply is new enough or at minimum ATX and EPS specs for the board ? I tried a generic older ATX PSU on a socket 775 and it would not boot at all until I changed to a newer PSU.

Horun wrote:

Are you sure your power supply is new enough or at minimum ATX and EPS specs for the board ? I tried a generic older ATX PSU on a socket 775 and it would not boot at all until I changed to a newer PSU.

Yes, the psu works with the other 775 platform, I tried another psu and it does the same...
I really can't understand what's wrong :\

Bump, I noticed that the issue is triggered by the p4 connector, if I start the mb (which doesn't work anyway) without the p4 connector it stays on but if I do with 4 pin connector it turns on and then off.
All every other components are confirmed working.
Any advice will be appreciated.

Oh dear, I finally solved the problem.
I didn't know what was wrong but here is my solution:
I turned on the system without the p4 connector plugged, the system wasn't turning off, at this point I quickly connected the p4 connector and it didn't turn off, a long series of short beeps (cmos error probably) but still black screen, at this point I turned off the psu, kept the p4 connector inserted on the mb, turned on the psu, pushed the power button and the system booted fine.