Computer Shutting Down Randomly

So my computers is shutting down randomly. At first it was Bluescreening, then it just stopped and now it just instantly shuts down. It does this randomly at first it was when i made it work such as playing games with graphics all the way up. The computer worked fine for a year my friend built it for me then just bam now its doing this. Now its just shutting off when its on the desktop not even being used. My 20mm fan on the side also burned out about the same time this started happening.

Things ive tried/ done.
-Removing dust from computer.
-Ive ran Cpu Burn x4 had all 4 cores running 100% Cpu while watching Speedfan it rose 30 degrees and was fine i ran it for 5 mins.
-I ran Furmark for a good 5 minutes it was also fine.
-I Reinstalled Windows, and all drivers.
- Reset my Bios to defaults

Yesterday i ran all these tests: Cpu brun in, Furmark, i played Oblivion Max Graphics RUnes of Magic Max Graphics World of warcraft Max Graphics, Minecraft. Had no problems everything was fine then today it just starts shutting off on the desktop not doing anything.

Heres my computers spec's

Im running windows 7 64 Bit


CASE:NZXT Crafted Series Vulcan Black Steel Gaming mATX Computer Case
DISKDRIVE:LITE-ON Black 24X DVD+R 8X DVD+RW 12X DVD+R DL 24X DVD-R 6X DVD-RW 12X DVD-RAM 16X DVD-ROM 48X CD-R 32X CD-RW 48X CD-ROM 2MB Cache SATA 24X DVD Writer LightScribe Support
OS:Microsoft Windows 7 Home Premium 64-bit 1-Pack for System Builders - OEM
HEATSINK:Scythe SCSK-1100 100mm Shuriken Rev. B 3 Heat Pipes CPU Coole
MOBO:MSI 890GXM-G65 AM3 AMD 890GX HDMI SATA 6Gb/s USB 3.0 Micro ATX AMD Motherboard
GPU:HIS H587FN1GD Radeon HD 5870 1GB 256-bit GDDR5 PCI Express 2.1 x16 HDCP Ready CrossFireX Support Video Card
PSU:CORSAIR HX Series CMPSU-750HX 750W ATX12V 2.3 / EPS12V 2.91 SLI Ready CrossFire Ready 80 PLUS SILVER Certified Modular Active PFC Power Supply
CPU:AMD Phenom II X4 955 Black Edition Deneb 3.2GHz OC to 3.7
RAM:G.SKILL Ripjaws Series 8GB (4 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600
HD:Seagate Barracuda 7200.12 ST3500418AS 500GB 7200 RPM
THERMAL PASTE: Arctic Silver 5 Thermal Compound
 
"My 20mm fan on the side also burned out about the same time"...
Do you mean 120mm? Did you remove or disconnect this fan from the computer? Try replacing the power supply first
 
Yeah 120mm I meant. I disconnected it since its ben burned out.

Also is there any way for me to run a test on my power supply before i go replace it.
 
"Also is there any way for me to run a test on my power supply before i go replace it?"...
With your computer's problem, testing the power supply would not prove anything. Who makes your PFC (Power Factor Correction) power supply and what is its wattage rating?
 
PSU:CORSAIR HX Series CMPSU-750HX 750W ATX12V 2.3 / EPS12V 2.91 SLI Ready CrossFire Ready 80 PLUS SILVER Certified Modular Active PFC Power Supply
 
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