Alright, that means it is not likely memory, but it does not rule out the possibility entirely. Memtest86+ only tests certain memory stress scenarios. Windows causes stress in different ways than Memtest86+, so sometimes it helps to test one module at a time by just doing your normal routine in Windows and seeing if it crashes. You want to do your normal routine for as long (or better, twice as long) as it normally takes for a crash to occur while doing the things that normally cause crashes.

Did you re-seat the graphics card?