Is it my motherboard or RAM sticks?

[napsterv]

This the whole backstory below.

Spoiler

This is the question I posted on Tom's Hardware...

So in the morning my PC was running fine, shut down properly - no abrupt shutdowns. In the evening when I tried to boot it up, the following happened:-

I press the power button, the fans spin up, lights come on and after about 5-8 seconds it shuts down. I press the power button again...nothing. Again...nothing. Waited for about 3-5 minutes pressed the power the power button again same thing happens;
-the fans spin up, lights come on and after about 5-8 seconds it shuts down. I press the power button again...nothing. Again...nothing.

No POST. No BIOS screen nothing

I stripped everything apart and assembled bare minimum to check for hardware defects. Mobo,PSU,CPU and a stick of RAM.

Same thing happens. I touched the CPU and can feel a little warm so I assume my CPU is not dead. I ran the paper-clip test on my PSU and it runs fine.
I found the solution myself i.e enabling 'dummy load' in the BIOS. Or I thought so.

The above Ramayan happens again sometimes and I realized that if I wait 15 mins or so the PC boots up properly.
I've ran memtest86+ and RAM is not an issue.

I've already RAM'ed my PSU and this is happening on the new PSU too(Seasonic SII2 620W)(July 2015 Manufactured).

SO I am assuming there's something wrong with the power in my house. I have a switch board with 25A/240V.AC where everything's connected.
I stay in Mumbai btw. Do I still need a UPS? I thought UPS was a necessity in rural areas where the power is unstable.

Update: (Doesn't work)
Another discovery I made today is that when I press the reset switch immediately after power switch the PC booted up properly.

The problem is a real mystery.

Well I got a UPS and surprisingly the problem still persists. While messing around today I(again) discovered that when I removed a RAM stick, the PC booted up. Then I reseated it again and it still boots. I changed the channels. Ran memtest86 again...0 errors.
The boot failure only happens when the PC is started after several hours(i.e cold boot)

If anyone could help me solve this problem I will donate 101rs in their name in the nearest temple.

 

[DK_WD]

Hi [MENTION=286233]napsterv[/MENTION],

Based on your experience, it might be a MOBO issue. To confirm the problem, I'd suggest you to try the same MOBO on a different computer and put under observation for at least 8 hours. If the problem still occurs in different PC, then its a MOBO issue, otherwise it's a RAM issue.