CPU over voltage error on replaced Asus H81M-CS motherboard

This is a follow-up question to this question.

I initially thought of updating that question, but it started to get too ugly so starting a new independent thread.

First some context

My Current Rig

• 
  ■ Motherboard: Asus H81M-CS
  ■ Processor: i5-4440 3.1Ghz
  ■ Ram: Kingston hyperx fb-dimm
  ■ SSD: Kingston SSDNow 300 (128GB)
  ■ HDD: WD 1TB
  ■ Graphics Card: GTX 750Ti
  ■ PSU: iBall zps290

I also had a Netgear router that connected to the desktop. There was one main LAN cable that came from the ISP to the router and another that connected the desktop to the router. Recently some high voltage power lines outside came in contact with the ISP Lan cable, making it a live wire that destroyed everything in its way. The ISP bus mounted nearby exploded and so did my router. Before dying, my router passed on some of the surge to the motherboard which damaged it along with the keyboard and mouse as the USB ports were just near the LAN port.

The router itself along with my UPS were both connected to the same spike guard. The router I think shorted the spike guard too along with a tripper (something like a fuse) in my apartment. So to summarize, the ISP Lan became a high voltage wire, destroyed my router, but a few moments after the router had passed on the surge to my motherboard via LAN and also the spike guard it was connected to. This went on to the mains of my house.

I wasn't very sure as to how much damage the desktop had taken, I was only sure that the MoBo is gone and so has my keyboard and mouse. As my motherboard is under warranty I took it to the service center. The service center asked me to retain the CPU and 1 RAM stick when handing it over to them so they could validate if the CPU or RAM were causing any problems as well.

I just got it back today, at the center they connected it to a monitor and showed the BIOS load confirming the new mobo was fine. I also asked them to reconnect it to my cabinet and other components as I did not want to void the warranty. After this, the guy also removed the heatsink to show me that my original CPU was intact. While doing this, he also wiped off some thermal grease from the CPU chip to show me the details, however, there seemed to be some on the heat sink, so I didn't take it that seriously.

Satisfied I headed home and connected it. It said "new CPU detected" I got into setup, loaded the default settings and continued to boot. It proceeded to boot, started to load windows and then just as the loading screen appeared went off. On starting it again, it showed the start screen (the one with "press F2 or Del to enter BIOS") and restarted again. It did this by itself a couple of times and then displayed a "CPU over voltage error" along with a "Press F1 for setup" and restarted again.

As of now

At the first time, I try to start it, it lets me get into BIOS, check settings, etc and after a few seconds or a min of which it turns off and repeatedly restarts. After a few automatic restarts, it shows the "CPU over voltage error".

If I don't get into BIOS at the first start, it goes to the windows loading logo and then restarts.

Things I have tried so far

• 
  ■ I noticed the service center guys had mixed by the cabinet's power indicator LED (-) and(+) connectors on the motherboard. Basically connected (+) to the (-) pin and vice versa. I fixed this.
  ■ Resetting BIOS (Both using a jumper and also by removing the CMOS battery and draining the system of power)
  ■ Connect the system to a different PSU (Intex Techno 450)
  ■ Booting into a Linux Live disk via a USB CD Drive

Resetting the BIOS did not help, it continued to behave in the same manner as before

When I connected to a different PSU, it seemed to last much longer than before. So much that I started to believe it was the previous PSU that was causing all the trouble. I went into BIOS, checked every setting I could. Searched if there was something I need to change and also kept a watch on the CPU temp. It started at around 40c or 41c and went up to roughly 46c.

I then turned off the machine, connected the USB CD Drive and attempted to boot into Linux, it started to load, went on for a while but at the Linux loading screen again began to restart. It restarted and showed me the CPU over voltage error again.

I then reconnected my old PSU, booted into BIOS and checked the CPU temp, it started at 37c and went on to about 43c and restarted as before.

I'm now exhausted of what more can be done.

Questions

■ Could the mixed up power LEDs (+) and (-) have caused this
■ Given it allows me to initially boot into the BIOS and then start the restarting process, is it possible that the actual issue is the CPU heat and not the voltage. If yes, why did it go to 46c on one PSU and 43c on another PSU before restarting
■ The service center guy had wiped off a bit of the thermal grease to show me the CPU details. Could this be caused due to lack of thermal grease.
■ As my UPS was also connected to the spike guard which was shorted, is it possible that the UPS is causing issues. (I highly doubt this, as it seems to be working fine and is also powering my monitor which works ok. Also the PSU itself should be regulating it before it reaches the CPU)
■ Is it possible that the new Motherboard is faulty as well