Random BSODs Appearing To Be Memory Related

I bought a new computer in Feb 2012 and the people that I bought it from put it together and I installed Windows 7 Professional 64 bit. Within the first week I was getting lots of random blue screens but being busy I couldn't deal with it and after the first week, then it was fine for about 2 months. I still have it under warranty.The blue screens were getting much more frequent, did memtest86 and had TONS of errors and took it in they said the ram was bad so they took out the bad ram and I've got it running now still with 8gigs.Took it home and every couple of days or hours or weeks I would get a blue screen related to memory such as MEMORY_MANAGEMENT or PAGE_FAULT_IN_NONPAGED_AREA etc. The people I purchased it from told me that they wouldn't look at it again until I've reinstalled Windows again from scratch. So I did. Same thing, random blue screens usually pointing to memory and at random times too (sometimes running a lot of things, other times it's been idle). I do shut my computer down every night.I decided to do another memtest86 and this time the memory seemed fine. Did chkdsk and it was fine. The people that I bought the computer from then took it back, looked at it for a day and said it must be the mouse, ethernet, power, keyboard, monitor, printer or something connected and that they wouldn't look at it until I'd swapped all that stuff.So I bought new speakers, new mouse, disconnected printer, new cables and a new ethernet cord (didn't buy a new monitor). Still getting random blue screens. I don't think it's related to a piece of hardware as I am running them all on another Windows 7 Pro 64 bit machine with no issues but just to be safe I swapped them all (except monitor).