Computer Random Crashes

[Antanous]

Hi all Iam in need of that magic answer,
my pc will randomly crash (some times many days apart) and then reboot some times will reboot fully ,
and some times it will cycle into another reboot after about 5 seconds.
I have run aida 64 , cinebench_r15 with No issues.
No error codes are displayed or heard.
All components have been removed and tested,
No over clocking has been done at all on the system
All fittings have been checked too, the only option I can think of is my motherboard is
on it way out. friends have just said to upgrade the pc but sadly I cant afford a whole new 
system as I would not want to use these parts on a new system without finding the fault.
 
Please any advice is welcome.

MB: Asrock X79 Extreme 6 (running latest Bio's)
PSU: Thermaltake 850w Toughpower
Ram: 4 x 8gig Kingston hyper X 1600Mhz
Cpu: i7-3820 socket 2011

SSD: Kingston Hyper X 240Gig,
HDD: 1x 2 Tb Seagate Barracuda
cd drive: 1x dvd sata drive

Graphics: 2x amd HD7970's in crossfire

fans: 2x120mm front and rear 

[CyberMist]

My friend, have u checked PC cooling?  Maybe PC require some hardware cleaning.Check  CPU/GPU cooling.  
Next its possible that issue u have is  due OS/drivers.  Try to restore/recover for last days  when PC worked fine.. 

[Antanous]

pc is clean and showed no heat issues at all during last nights aida 64 tests

or previous tests, drivers are all up to date as of february 2014 when the last update was made by asrock

and downloaded from asrock site

Bio's is the latest from asrock.

running windows 7 ultimate 

[tkell]

mine would also crash but at least my MB would let me know on the reboot that it was from an Power surge, after I got a AX860 things seemed to be all good, that was upgrading from a RM850.

[Bozol]

Your power supply might be starting to fail, I've had similar problems with my GS700 so I borrowed another psu from a friend and the problem stopped occuring. So i went with the RMA and the place at which I bought it said I can pick another PSU within the price of the old one or choose a better one and pay the difference since GS700 wasn't being sold anymore. Went with HX750i and've been golden ever since.

[Antanous]

after a bit I saved up and got a Corsair RM1000, so far no issues at all

looks like the old Thermaltake 850 was the issue .