Random Computer Hang

i did a search through the forums to see if anyone else has had this issue but i could not find the exact problem.
before i go into details, here are the system specs. please note nothing has been over clocked.

cpu-intel core i7-2600k processor
motherboard-gigabyte intel z68 atx ddr3 2133 lga 1155 motherboards ga-z68x-ud3h-b3
gpu-evga geforce gtx 560 ti super-clocked 1024mb gddr5 pci-express 2.0 graphics card
memory-corsair vengeance blue 16 gb ddr3 sdram dual channel memory kit cmz16gx3m4a1600c9b
primary hard drive-intel 510 series (elm crest) ssdsc2mh120a2k5 2.5" 120gb sata iii mlc internal solid state drive (ssd)
slave hard drive-western digital caviar green 2 tb
sound card-creative labs sb0570l4 sound blaster audigy se
psu-1 x ocz zs series 750w 80plus bronze high performance power supply compatible with intel sandy bridge core i3 i5 i7 and amd phenom
cpu cooler- zalman cnps9500 at 2 ball cpu cooling fan/heatsink
media burner-lg black 12x bd-r 2x bd-re 16x dvd+r 12x dvd-ram 10x bd-rom 4mb cache sata internal 12x blu-ray disc rewriter wh12ls38
card reader-rosewill rcr-ic001 40-in-1 usb 2.0 3.5" internal card reader w/ usb port
case-rosewill challenger black gaming atx mid tower computer case
operating system-windows 7 professional 64-bit

i started this build in december and the hang has been happening more and more frequently. when playing a game, bf3, in my case, everything works perfectly, cpu and gpu stays cool, i have the windows widgets and a readout on my keyboard that uses core temp to see live temps.
however, just watching a video on Internet or browsing a site, or just listening to music, the system will freeze with the latest image on the screen and if sound was on, a .05 loop of the sound will keep playing. this happens at random times, nothing predictable, and i cannot replicate it. i cannot alt-tab, or ctrl-alt-delete out of it. both keyboard and mouse go dead and the only way to break the freeze is to hit the reset or power button. on some occasions i will get a bsod, but i think it has only happened 2-3 times, where as the hang has occurred at least 20+ times in the last month and a half.

here are some of the things i have tried.

-ran memtest86 for 14 hours: no errors
-disabled on board audio in the bios
-uninstalled realtek drivers
-updated video card, and sound card drivers
-ran atitool scan for artifacts for 8 hours: none found
-ran prime95 for 4 hours: stayed below 55c no errors.
-ran chkdsk
-messed with my power plans
-enabled and disabled fast boot in the bios
-ran full system scans with avast, ms security essentials, superantispyware, and malwarebytes: nothing found but tracking cookies
i have done more but i cannot remember right now, will post when it comes back to me.

my next step is trying a new power supply, the 750w may not have enough juice, but i do not have one to test with currently. i am eying the 1200w x-series from seasonic but i want to make sure it is not something else before i plunk more money down. i am willing to try any suggestions.

edit: forgot to add that this build originally started with a 96gb ssd which i had win7 loaded on. i felt it was too small so i upgraded to the larger one. however when i had the smaller ssd installed the same symptoms were present.