Pc freezing without errors or bsod

So my pc has been randomly freezing and locking up after an hour or two of use and i cant figure out why. I have updated my graphics card and bios. I have tried both ram sticks in individually into the first slot, so unless both ram sticks went bad at the exact same time, they should be ok. I did try to run memtest overnight, but upon waking i found that the pc had restarted. I have cleaned out the pc of dust, and the heat seems fine on cpu, gpu, and mobo. I have run a full av scan with malware bytes and cleared up registry and temp files with ccleaner. I dont really know what else to try at this point, any help would be great.
specs:
windows 7 professional 64 bit
intel i5-2500k cpu @ 3.3ghz
2 4gb sticks corsair vengeance ddr3 ram
p8p67 pro rev 3.1 asus motherboard
2 nvidia 560 ti's in SLI
Crucial M4 CT064M4SSD2 2.5" 64GB SATA III MLC Internal Solid State Drive (SSD)

Please let us know what it says in the system event prior to the freezing problem.

the last few events in the event viewer i can see are
kernel-general eventid 13
kernel-power eventid 109

those are followed by a lot of
service control manager eventid 7036

Have you tried the ff:

- chkdsk of the hard drives

- sfc /scannow:

How To Use SFC Scannow to Repair Windows System Files

- msconfig, disable startup and services to see if one of the programs or services started up is causing the problem.