had same sort of problem years back,tryed everything to get pc run right and kept frezzing, i ended up swaping bits in me pc as i could afford them lol,went thro a new motherbords,new memorry, new cpus, new psu, new gfx,new hdds tryed loads of diferent parts in me pc and it was all the same it just frozz it cost me arm and leg i had enough parts to build about 3 pcs at time with the amout of stuff i brought trying to work out the prob lol thought it could have been somit like the parts didnt match each other but was not to wise then lol and it passed all the benchmark tests each thing did.in the end fount out problem which didnt even cross my mind at the time it was the case it was all sitting in asoon as swaped the case it all worked fine lol the power button most of been arking in some way cuzing the frezz, i lernt a valuble lesson from it tho try to work out the prob before ya just jump in lol me advice to ya would be try to strip everything to bare minum eg run one stick memory use onbord gfx if bord got it so on unplug unnessery cards and usb ports then try and do a fresh renstall with out copying over files do a complate format then try