CPU Multiplier underclocking itself with second HDD

[IggyJ]

So I'm running a Xeon x5670 on a Sabertooth X58 board, overclocked to 4GHz.
For whole year it's been running perfectly fine, stable and with no throttling or problems of any sorts.

Recently I've installed a second HDD to my system, and ever since this has started to happen:
First my processor will reduce its multplier from x22 to x12, and stay locked at 12.
I then proceed to turning off my PC, but when I try to turn it back on it won't post.
The CPU LED on my motherboard turns red, and I cannot post into the BIOS.
The only way to fix this is by removing my second HDD and turning it back on.
Everything works perfectly fine, even when I put the second HDD back in.
A few days later the whole problem starts from the beginning and I have to start all over.

Things I've tried so far (without success):
- Resetting BIOS to default.
- Clearing CMOS (using jumpers)
- Lowering multiplier speed of processor.
- Changing motherboard battery.
- Repasting my processor (incase there was any thermal throttling!)

My BIOS settings:
- Ai Overclock Tuner: XMP
- CPU Ratio Setting: 22
- Intel SpeedStep Tech: Disabled
- BLK Frequency: 182
- DRAM Freqency: DDR3-1095MHz
- CPU Voltage: 1.31875
Everything else set to default.

My Specs:
Intel Xeon X5670 (supposedly at 4GHz)
24GB RAM
Asus Sabertooth X58
GTX 760 2GB
1 x HDD 500GB
1 x HDD 1TB
Corsair H80i GT
Antec 500W PSU