Random crashing, no bsod

[chalo1000]

Hello,
I built this computer a few years back and have recently been getting random freezes / lock-ups with a buzzing noise, but no bsod
specs:
Intel core 2 quad q6600 @ 2.4Ghz
Asus p5n-t deluxe
OCZ DDR2 PC2-8500 FATAL1TY 4GB DUAL CHANNEL
OCZ vertex 3 120Gb ssd
WD 1TB HDD
Rosewill 650w PSU
Nvidia Geforce gts 250 SLI

I've tried replacing the psu, but no luck. I ran memtest for a good 2 hours but no errors happened. Also updated my SSD's firmware, no results either. All of my chipset, video, onboard audio drivers, and applied bios latest bios update. Oh and my temps an everything range from 40C - 55C.
All help will be appreciated.

 

[butremor]

Hi download this application and run scan on yuor HDD
http://support.wdc.com/product/download.asp?groupid=613&sid=3&lang=en

 

[chalo1000]

Hi download this application and run scan on yuor HDD
http://support.wdc.com/product/download.asp?groupid=613&sid=3&lang=en

Thanks, but my HDD passed both the quick and extended tests.
Any other suggestions?

 

[Diademist]

Hmm, if PSU, HDD or RAM are not the causes, then i suggest to give it a test with Prime95. And also try to monitor the temps. And to mne it looks like faulty MOBO (only a possibility).