New PC Random lockups

[MMXMonster]

A friend of mine has a PC purchased from CyberPower it has the following components:

Intel I7 2600k CPU
16Gigs of G-Skill Memory
NVidia GeForce GTX 560 1Gig
Gigabyte Z68 Mainboard
2 Terabyte SeaGate Drive
Windows 7 Home Premium

I took the machine home when he first started having problems... Windows was corrupt and had to re-install from the ground up including all new drivers. After which I discovered the Drive was failing (ran their diagnostic tool SeaTools and it had bad sectors). I was able to get Seagate to warranty the drive. Re-installed AGAIN and ran the system for a few days and had no problems. But, I was contacted today that the old problems of freezing and windows having problems starting have re-occured.
He said he ran memtest for 7 passes and no problems were found.

Question, can the power supply that they put in, which they claim to be 800w be the cause. I know they dont use high quality PSUs. Can unclean power from the outlet cause the drop outs and lockups? The HD was tested again and it passed all tests, unlike the previous drive that failed 2 of the 3 SeaTools tests.
He primarily uses it to play Diablo 3, Carrier Command and surf the web.
He has another PSU but with lower wattage to try and I am going to have him put in one stick of memory and see if anything changes. What else can be suggested to figure this out. Any diagnostic software that can test the mainboard?

 

[ronintexas]

I recently built a new computer for my wife. I purchased 2 RAM sticks in a kit, and was experiencing similar issues - when trying to install Windows - it would randomly crash or display a BSOD. Finally traced it down to a defective RAM stick.

It passed all memory tests and POST tests - but Windows 7 would not install or startup properly with the 2nd RAM stick inserted (2 X 4GB).

I could not get the memory to fail any tests - other than the BSOD/lockup in Windows when the stick was inserted.