PC problems

Hi guys i am tiny bit of a noob but have come pretty far i built my first PC successfully at the start of the year for gaming mainly. It ran great no troubles. then kind of caught the hardware bug and wanted to go upgrading things so i started with what i thought was the weakest point of my original build and purchased a new cpu and mother board ever since i replaced these components i have uncounted bsod i never get the same fault code gaming is fine but browsing the net , idling and installing patches it would randomly blue screen i have searched high and low on google to no avail so far i have made sure all drivers are up to date re flashed the bios to the latest and had 3 clean installs of windows 7 also removed the graphics card aswell .

it gets interesting when i ran memtest i think i wouldn't know to be honest but my intial run of memtest came up with 2042 faults so i was kind of pleased i thought i found it .so proceeded removed 2 sticks of ram and marked them ran memtest multiple times for about an hour each time no errors . so i removed those to sticks and put the other sticks that i removed first back in tested them multiple times for about an hour also expecting a fault but i didn't get one I'm kind of stuck and frustrated limited tools and knowledge. I'm thing of taking the computer back to the store but hesitant as im keen to learn but dont want to spend too much money on software or tools i will probably never use again.

Original build (good one no troubles)

intel i5 3570k

gigabyte generic mobo nothing special

evga gtx680 sc

g skill 4x4gb 1600mhz ram

1tb hdd 

650w psu

 

current rig (trouble)

intel i7 4770k (new)

gigabyte GA-Z87-OC (new)

evga gtx60 (reused) i am running sli now but bsod where there before sli and don't think its graphics card

g skil 4x4 gb (reused)

1tb hdd (reused)

seasonic 860w Psu

note i have not overclocked this yet wanted to wait and make sure system was stable first so i haven't messed around with bios only to make sure all the values where correct and should say if i run only 2 sticks of ram i haven't encounted a blue screen yet if someone could point me a direction that would be great and i could re download who crashed if you would like to see fault codes. sorry soo long winded but its been a saga i didn't want to take the parts back to find out it's not them at fault.

rma the ram kit. If it threw errors once, its toast. 

cheers thanks man will do