Issues with Intel DG965WH Mobo

My younger brother has been using a PC I built a while ago with a Intel DG965WH mobo and Intel Core 2 duo Processor, after a while he has been wanted to play more intensive games so I decided to upgrade the RAM from 2gb to 4gb.

My issue now is the computer will not boot, at all, not even to BIOS.

So as I knew something was amiss, I started removing parts starting with the recently added RAM, no luck. Then the HDD, still no luck. Then the external Graphics card, again no luck. I have narrowed it down to either the mobo, processor or PSU, but the computer has been working fine for several years now. But now when I try boot up it doesn't even display the BIOS, just powers up,

In the PC is:
-Intel DG965WH Motherboard
-2gb DDR2 667 RAM (intergral)
-Western digital HDD x 2
-Nvidia GeForce 8400GS Graphics Card
-FSP Group 240v PSU
-Intel Core 2 Duo CPU
-Windows 7 Home Premium 32bit

Thank you in advance for your replies!