System Interrupts, decrease in performance

[Akti]

Today while playing video games my the framerates suddenly dropped significantly.
I suspected that the issue was with my GPU / CPU Overclock.

Restarted my Computer and the same issue persisted.
I cleared the CMOS thus resetting the bios to default.
That didn't solve the issue.

I removed my hard drive only leaving the SSD and removed some fans to decrease power consumption (I was thinking it could be my PSU)

I ran memtest86 and it completed with no errors.

I then checked the task manager and saw a process called "System Interrupts" was hogging 25-30% of my CPU usage.

Did some bechmarks and my passmark was down to 1400 from original 2600...

I tried to use Windows monitoring tools to see if a driver was causing this issue but couldn't point out a driver.

Even the Windows event logs don't have anything odd in them.

I decided to do a clean reinstall of Windows 8.1.
The issue still exists and I'm getting desperate here.

Here is a screenshot from the task manager:
http://i.imgur.com/hxPU3SJ.jpg

I'm running an FX-4100 CPU which I have overclocked to 4.4GHz and cooling it with a custom built water cooling loop.
My GPU is MSI GTX 750 TI Twin Frozr
My motherboard is a ASUS M5A99X EVO
2 x 4GB Kingston HyperX Genesis ram running at 1600Mhz
I have a Kingston SSD 128gb + 1TB Seagate hard drive.
My PSU is a Corsair CX600M

EDIT:

I ran memtest again did 5 passes with no errors so it's not the ram.

Here is a screenshot of HWmonitor
http://i.imgur.com/7pnMHzk.png

What is weird is that the 12 volts from my psu only showing up as 11.90 sometimes it went low as 11.75.
Could it be a faulty psu?

EDIT 2:

I just ran Windows Checkdisk and performed a clean boot.
Things got even crazier... The CPU usage is now at almost 100% all the time and the system is barely usable.

Here is a screenshot of the task manager.
http://i.imgur.com/FgNTR8f.png

EDIT 3:
Had some further issues.
Motherboard boot device led was red and stuck on bios logo.

Tested with another power supply.

The motherboard must be broken.

I need some input people!

 

[Akti]

Ok people.

Turns out the board was dead.
A chip controlling the sata, usb and cpu was partially burnt and this was causing all the issues.

Bad luck I guess.

 

[indsup]

Surprised it was starting at all. If you buy the exact same board you will not have to reinstall windows or anything. Good luck!!

 

[Akti]

Just a quick update.

Turns out the CPU was dead as well.
Ran PC-Check and it showed a mp symmetry test that had failed.
The system interrupts and high cpu usage continued even with the new motherboard.

I went and got myself a FX-6300 and installed it.
System interrupts now only taking 0 - 0.5% cpu usage (usb device causing it) and the benchmarks show normal scores now.
Before the new cpu the system interrupts used to hog 30-40% cpu usage and made the computer slow as hell.

I ran PC-Check again and it still showed a fail on mp symmetry test. Really odd since everything is working well with the new CPU.

I work as an IT-technician and I repair computers every day and yet my own system gave me more headache than any clients computer has ever done.

CPU failures are really rare so I didn't think that might be causing the issues.
It could be that the old mobo destroyed the CPU with it. Who knows.