I recently built a new PC using the following components:
Corsair 500W CX Series PSU
Sapphire HD 5670 512MB
Core i5 2500 3.3GHz Socket 1155
Asus P8H67-M H67 Socket 1155
OCZ 4GB (2x2GB) DDR3 1333MHz/PC3-10666
WD 640GB 3.5" SATA-III 6Gb/s Caviar Black Hard Drive
The build went smoothly apart from the RAM would only run stable at 1066MHz. I installed Windows 7 Ultimate and all my apps and everything was running great. Then after a few days the PC started randomly blue screening usually with either Memory_Management errors or Page Fault in non paged area. Shortly after I was unable to boot into Windows at all and non of the recovery options worked so I reinstalled windows but once again the same problems returned. I tried to test the memory using Memtest86 but I just got a blank screen when trying to boot off the disk. I tested the memory using the windows 7 memory diagnostic and no errors were reported. I also stress tested the Hard Disk using a utility from Western Digital but this past also. I have now installed Windows XP pro but still getting random crashes and general poor performance.